01 general microbiology

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General Microbiology

Microbiology

Department of

Basic Sciences

EMIS ITESM


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Unique characteristics of microbial groups:

- disease mechanisms,

- host responses, and therefore

- need for different interventions.

Types of cellular microorganisms

- prokaryotes

- eukaryotes.

http://archive.bio.ed.ac.uk/jdeacon/microbes/
http://archive.bio.ed.ac.uk/jdeacon/microbes/http://archive.bio.ed.ac.uk/jdeacon/microbes/http://archive.bio.ed.ac.uk/jdeacon/microbes/


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Classification

Karl von Linn (Lineo), botnico

Suizo del S. XVIII. (1707-1778)

Categoras taxonmicas:

Sistema Natural: organiz a los

seres vivos en categoras y acu

el sistema binomial: gnero y

especie.

King Philip Cuts Open Five Green

Snakes


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Kingdoms

http://www.as.wvu.edu/~bio21/Bacteria.html
http://www.as.wvu.edu/~bio21/Bacteria.htmlhttp://www.as.wvu.edu/~bio21/Bacteria.htmlhttp://www.as.wvu.edu/~bio21/Bacteria.html


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Niveles taxonmicos(To)

Keep -Kingdom

People -Phylum

Clean and - Class

Odor - Order

Free - Family

Get - Genus

Soap - Species


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Prokaryotes

Size 1m in diameter aprox.

Absence of a nuclear membrane.

Circular DNA 1 mm aprox. (prokaryotic chromosome) in the

nucleioid.

OPEN IN CLASS:

http://learn.genetics.utah.edu/content/begin/cells/scale/

http://www.biology.arizona.edu/cell_bio/tutorials/cells/cells2.html
http://learn.genetics.utah.edu/content/begin/cells/scale/http://www.biology.arizona.edu/cell_bio/tutorials/cells/cells2.htmlhttp://www.biology.arizona.edu/cell_bio/tutorials/cells/cells2.htmlhttp://www.biology.arizona.edu/cell_bio/tutorials/cells/cells2.htmlhttp://learn.genetics.utah.edu/content/begin/cells/scale/http://learn.genetics.utah.edu/content/begin/cells/scale/


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Bacterial morphology

http://2.bp.blogspot.com/-2ObAKvwnffA/Tn0_Y7Q4AiI/AAAAAAAAAxM/pVZ0YweLVSI/s1600/Tipos+de+bacterias.JPG
http://2.bp.blogspot.com/-2ObAKvwnffA/Tn0_Y7Q4AiI/AAAAAAAAAxM/pVZ0YweLVSI/s1600/Tipos+de+bacterias.JPGhttp://2.bp.blogspot.com/-2ObAKvwnffA/Tn0_Y7Q4AiI/AAAAAAAAAxM/pVZ0YweLVSI/s1600/Tipos+de+bacterias.JPGhttp://2.bp.blogspot.com/-2ObAKvwnffA/Tn0_Y7Q4AiI/AAAAAAAAAxM/pVZ0YweLVSI/s1600/Tipos+de+bacterias.JPGhttp://2.bp.blogspot.com/-2ObAKvwnffA/Tn0_Y7Q4AiI/AAAAAAAAAxM/pVZ0YweLVSI/s1600/Tipos+de+bacterias.JPG


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Prokaryotic Diversity

The of genes within a prokaryote:

468 in Mycoplasma genitalium,

4288 in Escherichia coli,

7825 in Streptomyces coelicolor

Mainly for energy generation, macromolecular synthesis, and cellularreplication.

The prokaryotic group encompasses a heterogeneous range ofspecialists, each adapted to a rather narrowly circumscribed niche.

G l Mi bi l


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Prokaryotic Communities

Consortia: arrangements of specialized physiological characteristics ofdifferent organisms that contribute to survival of the group as a whole. Eachtype is a clone.

The biology of the community differs substantially from that of a single cell.

- High cell number virtually assures the presence within the clone of at leastone cell carrying a variant of any gene on the chromosome. Where thegenetic variabilitythe wellspring of the evolutionary process callednatural selectionis assured within a clone.

The high number of cells within clones also is likely to provide physiologic protectionto at least some members of the group.

Extracellular polysaccharides, may allow cells within the interior to surviveexposure to a lethal agent at a concentration that might kill single cells.

http://www.microbiologybytes.com/blog/tag/quorum-sensing/
http://www.microbiologybytes.com/blog/tag/quorum-sensing/http://www.microbiologybytes.com/blog/tag/quorum-sensing/http://www.microbiologybytes.com/blog/tag/quorum-sensing/http://www.microbiologybytes.com/blog/tag/quorum-sensing/http://www.microbiologybytes.com/blog/tag/quorum-sensing/


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Biofilms

Indeed, in nature, microorganisms seldom live in the isolated single-species colonies. They more typically live in communities calledbiofilms.

A bacterial biofilm is a structured community of bacterial cellsembedded in a self-produced polymer matrix (glycosides) andattached to either an inert surface or living tissue.A biofilm also canbe considered a hydrogel, which is a complex polymer containingmany times its dry weight in water. Such biofilms can developconsiderable thickness (mm).

The bacteria located deep within such a biofilm structure areeffectively isolated from harmful factors in the environment, such asdesiccation, immune system cells, antibodies, and antibiotics.


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Biofilms Biofilms are common modes of existence for populations of different

species of bacteria

- Plaque on teeth: layers accumulate on teeth, where, the excreted by-products

of different species are used by other bacterial species for nutrients. Likewise,depending on the oxygen tolerance, different organisms position themselvesaccording to their gaseous requirements, as multi-species environment or as apopulation of a single species.

The close proximity of microorganisms within a biofilm might also have the

advantage offacilitating the transfer of genetic information by, for example,conjugation.

http://www.valam.com/?Page=Biofilm
http://www.valam.com/?Page=Biofilmhttp://www.valam.com/?Page=Biofilmhttp://www.valam.com/?Page=Biofilm


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Examples of Medically Important Biofilms

Oral streptococci and other bacteria attach to the surface ofthe cardiac valves toform a biofilm. Professional phagocytes are attracted to the site and attempt,unsuccessfully, to phagocytize the bacteria. The frustrated phagocytes thenrelease the tissue-damaging content of their lysosomes, resulting in aninflammatory reaction and the clinical picture ofendocarditis.

Endoprostheses, catheters, cardiac pacemakers, shuntvalves, etc.The microorganisms covered by fibrinogen, fibronectin,vitronectin, or laminin.

Staphylococci surface proteins, can bind specifically tothese proteins (fibrinogen, etc.) and proliferate. Theysecrete the biofilm matrix on the foreign body. Suchbiofilms represent foreign body-associatedinfectionfoci.

Plaque: certain oral streptococci (S. mutans) bind tothe proteins covering tooth enamel, and builda glucanmatrix out of sucrose. Other bacteria adhere to thematrix and form plaque, the precondition for destructionof the enamel and formation ofcaries.

http://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatments

http://entkent.com/biofilms.html
http://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://entkent.com/biofilms.htmlhttp://entkent.com/biofilms.htmlhttp://entkent.com/biofilms.htmlhttp://entkent.com/biofilms.htmlhttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatmentshttp://www.mayo.edu/research/discoverys-edge/heart-devices-infections-treatments


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Quorum sensing

Bacteria can communicate with one another and behavecooperatively.

Bacteria (of the same species act in concert by signalling to eachother and co-ordinating their behavior: quorum sens ing(from theLatin: sufficient members are present for voting).

The signals used fall broadly into two types, Gram positives tend touse small peptides whereas Gram negative bacteria use N-acylhomoserine lactones (AHLs).

Regulate: symbiosis, virulence, competence, conjugation, antibiotic

production, motility, sporulation and biofilm formation.

VER ESTE VIDEO!!!

http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.html

http://www.ncbi.nlm.nih.gov/pubmed/11544353
http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.htmlhttp://www.ncbi.nlm.nih.gov/pubmed/11544353http://www.ncbi.nlm.nih.gov/pubmed/11544353http://www.ncbi.nlm.nih.gov/pubmed/11544353http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.htmlhttp://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.htmlhttp://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.html


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Quorum sensing

This is a phenomenon in which bacteria monitor their own

population density through sensing the levels of signalmolecules, sometimes called autoinducers because theycan stimulate the cell that releases them.

The concentration of these signal molecules increases

along with the bacterial population until it rises to a specificthreshold and signals the bacteria that the populationdensity has reached a critical level or quorum.

The bacteria then begin expressing sets ofquorum-

dependent genes.

VER ESTE VIDEO!!!

http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_c

ommunicate.htm
http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.htmlhttp://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.htmlhttp://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.htmlhttp://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.html


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Quorum sensing

By using quorum sensing, the organism prevents

unnecessary activity until the appropriate time.By producing a virulence factor, for example

only when large numbers of the organism are

present, the total amount of virulence factor is

optimised and hence the bacteria stand agreater chance of having an effect.

http://www.pnas.org/content/97/16/8789/F3.expansion.html

Pl id
http://www.pnas.org/content/97/16/8789/F3.expansion.htmlhttp://www.pnas.org/content/97/16/8789/F3.expansion.html


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Plasmids

Plasmids: circular DS-DNA that replicates

independently of chromosome

Prokaryotes exchange their plasmids,

Of particular concern aredrug resistance

plasmids that may render diverse bacteriaresistant to antibiotic treatment.


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Survival strategiesSurvival strategies

Symbiotic relationships: ea.: nutritional exchanges among organismswithin the human gut that benefit both the microorganisms and their humanhost.

Parasitic interactions can be quite deleterious to the host.

The most widely distributed examples of bacterial symbionts appear to bechloroplasts and mitochondria, the energy-yielding organelles ofeukaryotes. A substantial body of evidence points to the conclusion thatancestors of these organelles were endosymbionts, prokaryotes thatestablished symbiosis within the cell membrane of the ancestral eukaryotichost.

B t i & A h b t i


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Bacteria & Archaebacteria

Before molecular evidence becameavailable, the major subgroupings ofarchaebacteria seemed disparate. Themethanogens carry out an anaerobicrespiration that gives rise to methane;the halophiles demand extremely highsalt concentrations for growth; and thethermoacidophiles require high

temperature and acidity.

It has now been established thatthese prokaryotes sharebiochemical traits such as cell wallor membrane components that setthe group entirely apart from allother living organisms. Anintriguing trait shared byarchaebacteria and eukaryotes isthe presence of introns withingenes.

http://www.iatp.org/files/Micro-organisms_Definitions_and_Options_under_.htm

http://mrwrightsclass.net/projects/period4/paige_maria_andreas/EUBACTERIA/eubacteria.html
http://www.iatp.org/files/Micro-organisms_Definitions_and_Options_under_.htmhttp://mrwrightsclass.net/projects/period4/paige_maria_andreas/EUBACTERIA/eubacteria.htmlhttp://mrwrightsclass.net/projects/period4/paige_maria_andreas/EUBACTERIA/eubacteria.htmlhttp://mrwrightsclass.net/projects/period4/paige_maria_andreas/EUBACTERIA/eubacteria.htmlhttp://mrwrightsclass.net/projects/period4/paige_maria_andreas/EUBACTERIA/eubacteria.htmlhttp://mrwrightsclass.net/projects/period4/paige_maria_andreas/EUBACTERIA/eubacteria.htmlhttp://www.iatp.org/files/Micro-organisms_Definitions_and_Options_under_.htmhttp://www.iatp.org/files/Micro-organisms_Definitions_and_Options_under_.htmhttp://www.iatp.org/files/Micro-organisms_Definitions_and_Options_under_.htmhttp://www.iatp.org/files/Micro-organisms_Definitions_and_Options_under_.htm


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The "true nucleus" of eukaryotes is only one of their distinguishing

features. The membrane-bound organelles, the microtubules, andthe microfilaments of eukaryotes form a complex intracellularstructure unlike that found in prokaryotes.

Microbial eukaryotesprotistsare members of the fourfollowing major groups: algae, protozoa, fungi, and slime

molds (non-pathogenic).

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/green.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/amoeba.html

http://gogglegirl.edublogs.org/2011/07/18/slime-molds/

Al
http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/green.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/amoeba.htmlhttp://gogglegirl.edublogs.org/2011/07/18/slime-molds/http://gogglegirl.edublogs.org/2011/07/18/slime-molds/http://gogglegirl.edublogs.org/2011/07/18/slime-molds/http://gogglegirl.edublogs.org/2011/07/18/slime-molds/http://gogglegirl.edublogs.org/2011/07/18/slime-molds/http://gogglegirl.edublogs.org/2011/07/18/slime-molds/http://gogglegirl.edublogs.org/2011/07/18/slime-molds/http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/amoeba.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/amoeba.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/amoeba.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/amoeba.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/amoeba.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/green.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/green.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/green.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/green.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/green.htmlhttp://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/green.html


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Algae

The term "algae" has long been used to denote all organisms thatproduce O2 as a product of photosynthesis.

One major subgroup of these organismsthe blue-green bacteria, orcyanobacteriaare prokaryotic and no longer are termed algae. Thisclassification is reserved exclusively for photosynthetic eukaryoticorganisms.

All algae contain chlorophyll in the photosynthetic membrane of theirsubcellular chloroplast.

Many algal species are unicellular microorganisms. Other algae may formextremely large multicellular structures. Kelps of brown algae sometimesare several hundred meters in length.

http://commons.wikimedia.org/wiki/File:Diver_in_kelp_forest.jpg

P t
http://commons.wikimedia.org/wiki/File:Diver_in_kelp_forest.jpghttp://commons.wikimedia.org/wiki/File:Diver_in_kelp_forest.jpghttp://commons.wikimedia.org/wiki/File:Diver_in_kelp_forest.jpg


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Protozoa

Protozoa are unicellular nonphotosynthetic protists:

Most flagellated (primitive)

Ancestors: algae that became heterotrophous and loss ofchloroplasts

Algae thus gave rise to the closely related protozoa

http://www.parbio.es/blog/trypanosoma-cruzi/

http://protist.i.hosei.ac.jp/PDB/Images/sarcodina/trichamoeba/sp_03.html

F i
http://www.parbio.es/blog/trypanosoma-cruzi/http://protist.i.hosei.ac.jp/PDB/Images/sarcodina/trichamoeba/sp_03.htmlhttp://protist.i.hosei.ac.jp/PDB/Images/sarcodina/trichamoeba/sp_03.htmlhttp://protist.i.hosei.ac.jp/PDB/Images/sarcodina/trichamoeba/sp_03.htmlhttp://www.parbio.es/blog/trypanosoma-cruzi/http://www.parbio.es/blog/trypanosoma-cruzi/http://www.parbio.es/blog/trypanosoma-cruzi/http://www.parbio.es/blog/trypanosoma-cruzi/


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FungiNonphotosynthetic protists growing as a mass of branching, interlacing

filaments ("hyphae") known as amycelium (molds, allergens).Septate and non septate (coenocyte)

Cell wall of chitin.

Yeasts: characteristic sexual reproductive processes and by thepresence of transitional forms.

http://www.davidmoore.org.uk/Sec04_14.htmhttp://www.bioidea.net/resources/deadly-molds/
http://www.davidmoore.org.uk/Sec04_14.htmhttp://www.bioidea.net/resources/deadly-molds/http://www.bioidea.net/resources/deadly-molds/http://www.bioidea.net/resources/deadly-molds/http://www.bioidea.net/resources/deadly-molds/http://www.bioidea.net/resources/deadly-molds/http://www.davidmoore.org.uk/Sec04_14.htmhttp://www.davidmoore.org.uk/Sec04_14.htm


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P i (P P) ll l


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Prions (PrP) non cellular.

A. Prions:

1. Prions are associated with subacutespongiform encephalopathies

like Creutzfeldt-Jakob disease.

2. Prions are naked proteinsthat havethe same amino acid sequence

as certain normal cellular proteins, butare folded differently.

3. The normal human cellular proteins(now referred to as cellular prion-likeproteins or Prpc) are coded for bycellular genes.

4. Once prion proteins gain entry into thehuman cells, modify the folding of

normal Prpc, and turn those proteins

into additional prions, and eventually

cause neurologic degeneration.

http://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroids

http://www.pandasthumb.org/archives/2005/10/of_prions_and_p.html

Viruses
http://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroidshttp://www.pandasthumb.org/archives/2005/10/of_prions_and_p.htmlhttp://www.pandasthumb.org/archives/2005/10/of_prions_and_p.htmlhttp://www.pandasthumb.org/archives/2005/10/of_prions_and_p.htmlhttp://www.pandasthumb.org/archives/2005/10/of_prions_and_p.htmlhttp://www.pandasthumb.org/archives/2005/10/of_prions_and_p.htmlhttp://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroidshttp://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroidshttp://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroidshttp://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroidshttp://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroidshttp://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroidshttp://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroidshttp://ap-bio-patrick-steed.wikispaces.com/Viruses,Prions,and+Viroids


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VirusesB. Viruses are obligate intracellular organisms (ie., they cannot be grown

outside a host cell).

1. Viruses are composed ofeither RNA or DNA surrounded by variousproteins. They may or may not have an envelope.

2. Viruses are noncellular. They take over host cells and, using the viral

nucleic acid, direct the synthesis and assembly of viral components to make

new virus.

http://210.36.18.48/gxujingpin/dwwswx/ev/3.htm

Viral families of human pathogens
http://210.36.18.48/gxujingpin/dwwswx/ev/3.htmhttp://210.36.18.48/gxujingpin/dwwswx/ev/3.htmhttp://210.36.18.48/gxujingpin/dwwswx/ev/3.htm


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Viral families of human pathogens

http://www.biomedcentral.com/1471-2180/5/19/figure/f6

Mi bi l G
http://www.biomedcentral.com/1471-2180/5/19/figure/f6http://www.biomedcentral.com/1471-2180/5/19/figure/f6http://www.biomedcentral.com/1471-2180/5/19/figure/f6http://www.biomedcentral.com/1471-2180/5/19/figure/f6http://www.biomedcentral.com/1471-2180/5/19/figure/f6


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Microbial Groups

C. Bacteria are prokaryotic cells.

1. Bacteria have 70S ribosomes, complex cell walls of

peptidoglycan (except for mycoplasmas), and no sterols (except in

Mycoplasma membranes).

2. Bacteria divide asexually by binary fission.

D. Parasites are eukaryotic cells.

1. The animal parasites are the protozoans, worms, and insects thatlive on other organisms.

2. These organisms have sterols in their cell membranes but do nothave cell walls.


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Microbial Groups

E. Fungi are eukaryotic organisms.

1. Fungi have complex carbohydrate cell walls

containing chitin, glucans, and mannans.

2. Fungal membranes have ergosterolas themajor sterol, allowing treatment with imidazolesand polyenedrugs.

3. Fungi include the yeasts, filamentous molds,

dimorphic fungi, and mushrooms.

http://palaeos.com/fungi/glossary/glossaryA.html

Dimorphic fungi
http://palaeos.com/fungi/glossary/glossaryA.htmlhttp://palaeos.com/fungi/glossary/glossaryA.html


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Dimorphic fungiMost fungal pathogens do take yeast forms once they

invade human tissues:

Courtesy of Nature Review Immunology, by Luigina Romani, @

http://www.nature.com/nri/journal/v4/n1/box/nri1255_BX2.html

Microbial Groups
http://www.nature.com/nri/journal/v4/n1/box/nri1255_BX2.htmlhttp://www.nature.com/nri/journal/v4/n1/box/nri1255_BX2.html


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Microbial Groups


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Bacteria


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Bacteria

Bacterial Taxonomy


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Bacterial Taxonomy

All organisms have a name consisting of two parts: the genusfollowed by the species (i.e., Homo sapiens).

Bacteria have been grouped and named primarily on theirmorphological and biochemical/metabolic differences.

However, bacteria are now also being classified according to their

immunologic and genetic characteristics.

We will focus on the Gram stain, bacterial morphology, andmetabolic characteristics, all of which enable us to rapidly determinethe organism causing a patient's infection.

Gram Stain


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Gram Stain

Bacteria are colorlessand its size is below the lightmicroscope resolution limit, colorful stains have been

developed to visualize them.

Gram stain, which separates organisms into 2 groups:gram-positive and gram-negative bacteria. This stain alsoallows the clinician to determine shape: round or rod-shaped.

For any stain you must first smear the substance to bestained (sputum, pus, etc.) onto a slide and then heat it to fixthe bacteria on the slide.

http://www.pc.maricopa.edu/Biology/rcotter/BIO%20205/LessonBuilders/Chapter%204%20LB/Ch4Lessonbuilder7.htmlhttp://www.biologie.uni-h GRAM STAIN VIDEO

Hans Christian Gram.

1853-1938
http://www.pc.maricopa.edu/Biology/rcotter/BIO%20205/LessonBuilders/Chapter%204%20LB/Ch4Lessonbuilder7.htmlhttp:/www.biologie.uni-hhttp://www.pc.maricopa.edu/Biology/rcotter/BIO%20205/LessonBuilders/Chapter%204%20LB/Ch4Lessonbuilder7.htmlhttp:/www.biologie.uni-hhttp://www.pc.maricopa.edu/Biology/rcotter/BIO%20205/LessonBuilders/Chapter%204%20LB/Ch4Lessonbuilder7.htmlhttp:/www.biologie.uni-hhttp://www.pc.maricopa.edu/Biology/rcotter/BIO%20205/LessonBuilders/Chapter%204%20LB/Ch4Lessonbuilder7.htmlhttp:/www.biologie.uni-hhttp://www.pc.maricopa.edu/Biology/rcotter/BIO%20205/LessonBuilders/Chapter%204%20LB/Ch4Lessonbuilder7.htmlhttp:/www.biologie.uni-h


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Gram Stain (Hans C. Gram, 1884)There are 4 steps to the Gram stain:

1) Pour on crystal violet stain (a blue dye)

and wait 60 seconds.

2) Wash offwith water and flood with iodinesolution. Wait 60 seconds.

3) Wash offwith water and then

"decolorize" with 95% alcohol.

4) Finally, counter-stain with safranin (a red

dye). Wait 30 seconds and wash offwith

water.

http://www.microbiologybytes.com/video/Gram.html
http://www.microbiologybytes.com/video/Gram.htmlhttp://www.microbiologybytes.com/video/Gram.html


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Gram Stain (differential staining)

When the slide is studiedmicroscopically, cells that absorbthe crystal violet that is retainedby thick layer of peptidogycan

and will appear blue. These arecalled gram-positive organisms.

However, if the crystal violet iswashed off by the alcohol, thesecells will absorb the safranin in

the peptidoglycan layerandappear red. These are calledgram-negative organisms.

G-positive G-negativehttp://www.youtube.com/watch?v=NWASSXDzHRs

http://www.youtube.com/watch?feature=endscreen&NR=1&v=Ly6j4pZFU3A

C V-Iodine

complex
http://www.youtube.com/watch?v=NWASSXDzHRshttp://www.youtube.com/watch?feature=endscreen&NR=1&v=Ly6j4pZFU3Ahttp://www.youtube.com/watch?feature=endscreen&NR=1&v=Ly6j4pZFU3Ahttp://www.youtube.com/watch?v=NWASSXDzHRs


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Gram Stain and Bacterial StructureCELL ENVELOPE.

The different stains are the result ofdifferences in the cell walls of gram-positive and gram-negative bacteria.

The cell envelope consists of the

cytoplasmic membrane, cell wall,outer membrane (Gram-negativebacteria only), and, for somebacteria, capsule.

The Role of the cell envelope. Inaddition to protecting the bacterial

cell, the cell envelope componentsplaya major role in adherence to orinvasion of human cells, virulence,and stimulation of the immuneresponse.

Limitations and significance???

Virulence, Inexpensive (accurate)

phylogenetic relationships (?)

Bacterial Structure: Membrane


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The bacterial cell membrane: phospholipids and upward of 200 different kinds ofproteins. Proteins account for approximately 70% of the mass of the membrane.

The cell membranes of the Archaea differ from those of the Bacteria. SomeArchaeal cell membranes contain unique lipids, isoprenoids, rather than fattyacids, linked to glycerol by an ether rather than an ester linkage.

At least 50% of the cytoplasmic membrane must be in the semifluid state in orderfor cell growth to occur.At low temperatures, this is achieved by greatly

increased synthesis and incorporation ofunsaturated fatty acids into thephospholipids of the cell membrane.

Archaea

EubacteriaIsoprene

units



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Bacterial Structure: MembraneThe major functions of the cytoplasmic membrane are:

1) selective permeability and transport of solutes;

2) electron transport and oxidative phosphorylation, in aerobic species;

3) excretion of hydrolytic exoenzymes;

.

4) bearing the enzymes andcarrier molecules that functionin the biosynthesis of DNA, cellwall polymers, and membranelipids; and

5) bearing the receptors and other

proteins of the chemotacticand other sensory transductionsystems.

http://pilusenergy.com/about/technology/
http://pilusenergy.com/about/technology/http://pilusenergy.com/about/technology/


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Bacterial Structure: MembraneBears the flagellum

http://www.arn.org/docs/mm/flag_dithani.htm

http://www.umass.edu/microbio/chime/pe2.76/pe/atlas/morphs/flaghook/index.htm
http://www.arn.org/docs/mm/flag_dithani.htmhttp://www.umass.edu/microbio/chime/pe2.76/pe/atlas/morphs/flaghook/index.htmhttp://www.umass.edu/microbio/chime/pe2.76/pe/atlas/morphs/flaghook/index.htmhttp://www.umass.edu/microbio/chime/pe2.76/pe/atlas/morphs/flaghook/index.htmhttp://www.arn.org/docs/mm/flag_dithani.htmhttp://www.arn.org/docs/mm/flag_dithani.htm


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Bacterial Structure:

Cell Wall

The internal osmotic pressure of most

bacteria ranges from 5 atm to 20 atm

as a result of solute concentration via

active transport. In most

environments, this pressure would be

sufficient to burst the cell were it not

for the presence of a high-tensile-

strength cell wall.

The bacterial cell wall owes itsstrength to a layer composed of a

substance variously referred to as

mucopeptide, or peptidoglycan.

http://www.detectingdesign.com/antibioticresistance.html

Bacterial Structure: Cell Wall
http://www.detectingdesign.com/antibioticresistance.htmlhttp://www.detectingdesign.com/antibioticresistance.html


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The layer just outside thebacterial cytoplasmicmembrane is thepeptidoglycan layerorcellwall. It is present in both

gram-positive and gram-negative organisms.

The peptidoglycan layerorcell wall is composed ofrepeating disaccharideswith 4 amino acids in a

side chain extending fromeach disaccharide.

Both gram-positive and gram-negative organisms have more than 1 layerprotecting their cytoplasm and nucleus from the extracellular environment,unlike animal cells, which have only a single cytoplasmic membrane composedof a phospholipid bilayer.

Disaccharide: N-acetylglucosamine G y N-acetylmumamic acid M united by -1,4

glycosidic bond.

Side chain: L-Ala, D-Glu, DAP (dipamelic acid) and D-Ala.

Peptide bond: between DAP and L-Ala


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The amino-acid chains of thepeptidoglycan covalently bind to otheramino acids from neighboring chains.This results in a stable cross-linkedstructure.

The enzyme that catalyzes theformation of this linkage is calledt ranspept idaseand is located in theinner cytoplasmic membrane. Theantibiotic penicillin binds to andinhibits this enzyme. For this reasonthe enzyme is also called penicillinbinding protein.

The gram-positive cell wall is verythick and has extensive cross-linkingof the amino-acid side chains. Incontrast, the gram-negative cell wallis very thin with a fairly simple cross-linking pattern.

Bacterial Structure: Cell wall


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Bacterial Structure: Cell wall

Peptidoglycan is a complex polymer consisting of three parts: a backbone,composed ofalternating N-acetylglucosamine and N-acetylmuramic acid; a set of

identical tetrapeptide side chains attached to N-acetylmuramic acid; and a set of

identical peptide cross-bridges.

Mode of action of lyzozyme: breakes the b-1,4 glycosidic bonds between each

disaccharide subunit.



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Cell wall

The backbone is the same in all

bacterial species; the tetrapeptide side

chains and the peptide cross-bridges

vary from species to species.

In many gram-negative cell walls, the

cross-bridge consists of a directpeptide linkage between the

diaminopimelic acid (DAP) amino

group of one side chain and the

carboxyl group of the terminal D-

alanine of a second side chain.

Each peptidoglycan layer is a single

giant molecule.

http://www.nature.com/nchembio/journal/v8/n1/fig_tab/nchembio.748_F4.html

Comparison G+ and G- bacteria
http://www.nature.com/nchembio/journal/v8/n1/fig_tab/nchembio.748_F4.htmlhttp://www.nature.com/nchembio/journal/v8/n1/fig_tab/nchembio.748_F4.html


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Comparison G+ and G bacteria

http://micro.cornell.edu/cals/micro/research/labs/angert-lab/low.cfm
http://micro.cornell.edu/cals/micro/research/labs/angert-lab/low.cfmhttp://micro.cornell.edu/cals/micro/research/labs/angert-lab/low.cfmhttp://micro.cornell.edu/cals/micro/research/labs/angert-lab/low.cfmhttp://micro.cornell.edu/cals/micro/research/labs/angert-lab/low.cfmhttp://micro.cornell.edu/cals/micro/research/labs/angert-lab/low.cfm


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Bacterial Structure: Cell Wall G+

The gram-positive cellenvelope has an outer cell wallcomposed of complex cross-linked peptidoglycan, teichoicacid, polysaccharides, andother proteins.

The inner surface of the cellwall touches the cytoplasmicmembrane. The cytoplasmicmembrane contains proteinsthat span the lipid bilayer.

The bacterial cytoplasmicmembrane (unlike that ofanimals) has no cholesterol orother sterols.

Teichoic acid acts as an antigenic

determinant, so it is important for

serologic identification

of many gram-positive species.

Bacterial Structure: Cell Wall.


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Bacterial Structure: Cell Wall.

Gram+ vs. Gram-

Aminoacid cross-linking between peptide side chains. This peptide link

represents the target for lysozyme and penicillin in Gram-positive bacteria.

Gram-negative bacteria contain LPSendotoxin- that blocks antibiotics, dyes an

detergents.http://textbookofbacteriology.net/themicrobialworld/Structure.html

Spirochetes

(spiral) syphilis,

lyme disease

Nisseria (cocci)

gonorrhea ,

meningococcus

http://textbookofbacteriology.net/themicrobialworld/Structure.htmlhttp://textbookofbacteriology.net/themicrobialworld/Structure.htmlhttp://textbookofbacteriology.net/themicrobialworld/Structure.html


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Most teichoic acids contain large amounts ofD-alanine, usually attached to position 2 or 3 of glycerolor position 3 or 4 of ribitol.

In addition to D-alanine, other substituents may beattached to the free hydroxyl groups of glycerol andribitol, eg, glucose, galactose, N-acetylglucosamine, N-acetylgalactosamine, or succinate.

Nice review of theichoic acid function

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2798926/

http://onlinelibrary.wiley.com/doi/10.1002/cbic.200900557/abstract

The term teichoic acids: polymers containing glycerophosphate or ribitol phosphateresidues connected by phosphodiester linkages and usually have other sugars and

D-alanine attached. Because they are negatively charged, teichoic acids are partially responsible for thenegative charge of the cell surface as a whole.

There are two types of teichoic acids: wallteichoic acid(WTA), covalently linkedto peptidoglycan, and membraneteichoic acid, covalently linked to membraneglycolipid. Because the latter are intimately associated with lipids, they have beencalled lipoteichoic acids (LTA).

The repeat units may be glycerol, joined by 1,3- or 1,2-linkages; ribitol, joined by 1,5-

linkages, or more complex units in which glycerol or ribitol is joined to a sugar residuesuch as glucose, galactose, or N-acetylglucosamine. The chains may be 30 or morerepeat units in length, though chain lengths often or less are common.

Bacterial Structure: Capsule & Glycocalyx
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2798926/http://onlinelibrary.wiley.com/doi/10.1002/cbic.200900557/abstracthttp://onlinelibrary.wiley.com/doi/10.1002/cbic.200900557/abstracthttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC2798926/http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2798926/


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Many bacteria synthesize large amounts ofextracellular polymerwhen growing in their natural environments. With one knownexception (the poly-D-glutamic acid capsules ofBacillus anthracis and

Bacillus licheniformis), the extracellular material is polysaccharide.

Glycocalyx is defined as the polysaccharide-containing material lyingoutside the cell. A condensed, well-defined layer closely surroundingthe cell that excludes particles, such as India ink, is referred to as acapsule. If the glycocalyx is loosely associated with the cell and does

not exclude particles, it is referred to as a slime layer.

http://basicbacteriology.blogspot.mx/p/external-structure-of-bacteria.html

http://www.sciencedirect.com/science/article/pii/S0305417909000849

The extracellular polysaccharide matrix, a component of biofilms, is clearly

demonstrated in ultrathin sections treated with tannic acid prior to contrast staining. The

bacterial glycocalyx (arrows) and proteoglycan granules (pg) are seen at high

magnification. Bar = 0.5 m.
http://basicbacteriology.blogspot.mx/p/external-structure-of-bacteria.htmlhttp://www.sciencedirect.com/science/article/pii/S0305417909000849http://www.sciencedirect.com/science/article/pii/S0305417909000849http://basicbacteriology.blogspot.mx/p/external-structure-of-bacteria.htmlhttp://basicbacteriology.blogspot.mx/p/external-structure-of-bacteria.htmlhttp://basicbacteriology.blogspot.mx/p/external-structure-of-bacteria.htmlhttp://basicbacteriology.blogspot.mx/p/external-structure-of-bacteria.htmlhttp://basicbacteriology.blogspot.mx/p/external-structure-of-bacteria.htmlhttp://basicbacteriology.blogspot.mx/p/external-structure-of-bacteria.htmlhttp://basicbacteriology.blogspot.mx/p/external-structure-of-bacteria.html


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Extracellular polymer is synthesized byenzymes located at the surface of the bacterialcell. Streptococcus mutans, for example, usestwo enzymes glucosyl transferase andfructosyl transferaseto synthesize long-

chain dextrans (poly-D-glucose) and levans(poly-D-fructose) from sucrose. These polymersare called homopolymers. Polymers containingmore than one kind of monosaccharide arecalled heteropolymers.

The capsule contributes to the invasiveness of

pathogenic bacteria encapsulated cells areprotected from phagocytosis unless they arecoated with anticapsular antibody.

The glycocalyx plays a role in the adherence ofbacteria to surfaces in their environment


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S. mutans adherestightly to toothenamel because of the glycocalyx.Bacterial cells of the same ordifferent species become entrappedin the glycocalyx, which forms thelayer known as plaque on the toothsurface; acidic products excreted bythese bacteria cause dental caries.

The essential role of the glycocalyx inthis process, and its formation fromsucrose, explains the correlation ofdental caries with sucrose

consumption by the humanpopulation. Because outerpolysaccharide layers bind asignificant amount of water, theglycocalyx layer may also play a rolein resistance to desiccation.


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Bacterial Structure (G+)


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Bacterial Structure (G-)

The gram-negative cell envelope has 3layers, not including the periplasmicspace. Like gram-positive bacteria, it has1) a cytoplasmic membranesurrounded by 2) a peptidoglycanlayer. 3) In addition, a gramnegative cellhas a unique outer cell membrane.

The inner cytoplasmic membrane (as ingram-positive bacteria) contains aphospholipid bilayer with embeddedproteins.

Gram-negative bacteria have aperiplasmic space between thecytoplasmic membrane and an extremelythin peptidoglycan layer. This periplasmicspace is filled with a gel that containsproteins and enzymes.



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Bacterial Structure (G )

The thin peptidoglycan layerdoes not contain teichoic acid,although it does have a smallhelical lipoprotein called mureinlipoprotein.

This lipoprotein is importantbecause it originates from thepeptidoglycan layerand extendsoutward to bind the unique thirdouter membrane.

This last membrane is similar toother cell membranes in that it iscomposed of two layers of

phospholipid (bilayer) withhydrophobic tails in the center.What makes it unique is that theoutermost portion of the bilayercontains lipopolysaccharide(LPS).

murein

http://www.ebc.ee/kaitsmised/2012/mag/Karl_Mumm.pdf

http://www.ebc.ee/kaitsmised/2012/mag/Karl_Mumm.pdfhttp://www.ebc.ee/kaitsmised/2012/mag/Karl_Mumm.pdfhttp://www.ebc.ee/kaitsmised/2012/mag/Karl_Mumm.pdf


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Lipopolysaccharide (LPS) is composed of 3covalently linked components:

1) Outer carbohydrate chains of 1-50oligosaccharide units that extend into thesurrounding media. These differ from oneorganism to another and are antigenicdeterminants. This part is called the O-specific side chain orthe O-antigen.

2) The center part is a water soluble corepolysaccharide.

3) Interior to the core polysaccharide is the thirdcomponent, lipid A, which is a disaccharidewith multiple fatty acid tails reaching into themembrane. Lipid A is toxic to humansand is

known as the gram-negative endotoxin.When bacterial cells are lysed by ourimmune system, fragments of membranecontaining lipid A are released into thecirculation, causing fever, diarrhea, andpossibly fatal endotoxic shock (also calledseptic shock).

Embedded in the gram-negative outer

membrane are porin prote ins, which allow

passage of nutrients. These are also unique

to gram-negative organisms.



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Lipid A consists ofphosphorylatedglucosamine disaccharide unitsto whichare attached a number of long-chain fatty

acids. Hydroxymyristic acid, a C14 fattyacid, is always present and is unique tothis lipid; the other fatty acids, varyaccording to the bacterial species.

The polysaccharide core is similar in allgram-negative speciesthat have LPSand includes two characteristic sugars,ketodeoxyoctanoic acid (KDO) and aheptose.Each species, however,contains a unique repeat unit.

The repeat units are usually lineartrisaccharidesor branched tetra- orpentasaccharides. The repeat unit is

referred to as the O antigen.

The O antigen is highly immunogenicin avertebrate animal. Antigenic specificity isconferred by the O antigen as this antigen ishighly variable among species and even instrains within a species.



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( )

The hydrophilic carbohydrate chains ofthe O antigen cover thebacterial surface and exclude hydrophobic compounds.

The negatively charged LPS molecules are noncovalently cross-bridged by divalent cations (ie, Ca2+ and Mg2+); this stabilizes themembrane and provides a barrierto hydrophobic molecules.

Removal of the divalent cations with chelating agents or theirdisplacement by polycationic antibiotics such as polymyxins andaminoglycosides renders the outer membrane permeable to largehydrophobic molecules.

http://www.atsu.edu/faculty/chamberlain/Website/Lects/Bacteria.htm

http://www.atsu.edu/faculty/chamberlain/Website/Lects/Bacteria.htmhttp://www.atsu.edu/faculty/chamberlain/Website/Lects/Bacteria.htmhttp://www.atsu.edu/faculty/chamberlain/Website/Lects/Bacteria.htm


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( )

Not all gram-negative bacteria have outer membrane LPS.Neisseria meningitidis, Neisseria gonorrhoeae, Haemophilusinfluenzae, and Haemophilus ducreyihave relatively short,branched glycans. Their structures more closely resemble thoseof the glycosphingolipids of mammalian cell membranes, and

they are more properly termed lipo-oligosaccharides (LOS).

These molecules exhibit extensive antigenic and structuraldiversityeven within a single strain.

LOS is an important virulence factor. Epitopes have beenidentified on LOS which mimic host structures and mayenable these organisms to evade the imm une respo nseof thehost.

http://glycob.oxfordjournals.org/content/8/2/113.full

Bacterial Structure
http://glycob.oxfordjournals.org/content/8/2/113.fullhttp://glycob.oxfordjournals.org/content/8/2/113.full


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Bacterial Structure

THE ACID-FAST CELL WALL

Some bacteria, notably the tubercle bacillus (Mycobacter ium tuberculo s is)and its relatives have cell walls that contain large amounts of waxes, complexbranched hydrocarbons (70 to 90 carbons long) known as mycolic acids.

The cell wall is composed of peptidoglycan and an external asymmetric lipidbilayer; the inner leaflet contains mycolic acids linked to an arabinoglycan andthe outer leaflet contains other extractable lipids. This is a highly ordered lipidbilayer in which proteins are embedded forming water-filled pores through whichnutrients and certain drugs can pass slowly.

This hydrophobic structure renders these bacteria resistant to many harshchemicals including detergents and strong acids or stains. If a dye is introducedinto these cells by brief heating or treatment with detergents, it cannot beremoved by dilute hydrochloric acid, as in other bacteria. These organisms aretherefore called acid-fast. (they must be heated and treated with an acid-

alcohol in order to stain them).

The permeability of the cell wall to hydrophilic molecules is 100- to 1000-foldlower than forE. coliand may be responsible for the slow growth rate ofmycobacteria.


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http://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.html

Bacterial Structure
http://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.htmlhttp://www.howtobio.com/2012/08/the-abc-of-acidfast-staining.html


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CELL WALLS OF THE ARCHAEA

Some Archaea have a rigid cell wall composed of polysaccharides

or a peptidoglycan called pseudomurein. The pseudomurein differs

from the peptidoglycan of bacteria by having L-amino acids rather

than D-amino acids and disaccharide units with an -1,3 rather than a

-1,4 linkage.

Archaea that have a pseudomurein cell wall are gram positive.

Archaeal cell wall.


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Phospholipids as have ester linkagesbetween fatty acids and the gylcerol

backbone.

This is not the case with Archaea.

Archaea use an ether linkage between

fatty acids and the glycerol backbone.

In addition, archaeal fatty acids can be

connected across the membrane(monolayer): bolaamphiphile.

http://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.html#!/2012/03/daily-newsletter-march-21-2012.html

Enzymes that attack cell walls
http://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.htmlhttp://microbiologymoocnews.blogspot.mx/2012/03/daily-newsletter-march-21-2012.html


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y The 1,4 linkage of the peptidoglycan backbone is hydrolyzed by the

enzyme lysozyme, (secretions: tears, saliva, nasal or in egg white).Gram-positive bacteriatreated with lysozyme in low-osmotic-strengthmedia lyse; if the osmotic strength of the medium is raised to balancethe internal osmotic pressure of the cell, free spherical bodies called

protoplastsare liberated.

The outer membrane of the gram-negative cellwall prevents accessof lysozyme unless disrupted by an agent such asethylenediaminetetraacetic acid (EDTA), a compound that chelatesdivalent cations; in osmotically protected media, cells treated withEDTA-lysozyme form spheroplaststhat still possess remnants of thecomplex gram-negative wall, including the outer membrane.

Bacteria themselves possess a numberofautolysins, hydrolyticenzymes that attack peptidoglycan, including muramidases,glucosaminidases, endopeptidases, and carboxypeptidases.

These enzymes catalyze the turnover or degradation of peptidoglycanin bacteria. These enzymes presumably participate in cell wall growth

and turnover and in cell separation, but their activity is most apparentduring the dissolution of dead cells (autolysis).

Enzymes that degrade bacterial cell walls are also found in cells thatdigest whole bacteria, eg, protozoa and the phagocytic cells of higheranimals.

http://www.proteopedia.org/wiki/index.php/Hen_Egg-White_(HEW)_Lysozyme

Protoplasts, spheroplasts and L forms
http://www.proteopedia.org/wiki/index.php/Hen_Egg-White_(HEW)_Lysozymehttp://www.proteopedia.org/wiki/index.php/Hen_Egg-White_(HEW)_Lysozymehttp://www.proteopedia.org/wiki/index.php/Hen_Egg-White_(HEW)_Lysozymehttp://www.proteopedia.org/wiki/index.php/Hen_Egg-White_(HEW)_Lysozymehttp://www.proteopedia.org/wiki/index.php/Hen_Egg-White_(HEW)_Lysozyme


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p p p

Removal of the bacterial wall may be accomplished by hydrolysis with lysozyme or byblocking peptidoglycan synthesis with an antibiotic such as penicillin. In osmoticallyprotective media, such treatments liberate protoplasts from gram-positive cells andspheroplasts (which retain outer membrane and entrapped peptidoglycan) from gram-negative cells.

If such cells are able to grow and divide, they are called L forms. L forms are difficult tocultivate.

L forms are produced more readily with penicillin than with lysozyme, suggesting the need forresidual peptidoglycan.

Some L forms can revert to the normal bacillary form upon removal of the inducing stimulus. Thus,they are able to resume normal cell wall synthesis. Others are stable and never revert. The factorthat determines their capacity to revert may again be the presence of residual peptidoglycan,which normally acts as a primer in its own biosynthesis.

Some bacterial species produce L forms spontaneously. The spontaneous or antibiotic-induced formation of L forms in the host may produce chronic infections, the organismspersisting by becoming sequestered in protective regions of the body.Since L-forminfections are relatively resistant to antibiotic treatment, they present special problems inchemotherapy.Their reversion to the bacillary form can produce relapses of the overtinfection.

http://www.indiana.edu/~oso/animations/An6.html

Lysozyme mode of action
http://www.indiana.edu/~oso/animations/An6.htmlhttp://www.indiana.edu/~oso/animations/An6.html


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Lysozyme mode of action

Penicillin prevents the formation of the interpeptide bond.

Lysine breaks the links between G and M.

Lysozyme

http://textbookofbacteriology.net/themicrobialworld/Structure.html

Bacterial Structure: Mycoplasmas
http://textbookofbacteriology.net/themicrobialworld/Structure.htmlhttp://textbookofbacteriology.net/themicrobialworld/Structure.html


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The mycoplasmasare cell wall-lacking bacteria containing nopeptidoglycan. There are also wall-less Archaea,

Genomic analysis places the mycoplasmas close to the gram-positive bacteria from which they may have been derived.

Mycoplasmas lack a target for cell wall-inhibiting antimicrobial agents

(eg, penicillins and cephalosporins) and are therefore resistant tothese drugs.

Some, like Mycoplasma pneumoniae, an agent of pneumonia,contain sterols in their membranes.

http://classes.midlandstech.com/carterp/courses/bio225/chap24/lecture4.htm

Bacterial Structure: Gram negative
http://classes.midlandstech.com/carterp/courses/bio225/chap24/lecture4.htmhttp://classes.midlandstech.com/carterp/courses/bio225/chap24/lecture4.htm


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Bacterial Structure

B t i l St t


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Bacterial StructureSURFACE PROTRUSIONS

A. Flagella(not found on all bacteria) are semi-

rigid, helical filaments made up of proteinflagelin. Counterclockwise rotation producesdirected motion; clockwise rotation producestumbling. Monotrichous, Lophotrichousand peritrichous..

The flagellins of different bacterial speciespresumably differ from one another in

primary structureThey are highly antigenic(H antigens), and some of the immuneresponses to infection are directed againstthese proteins.

The flagellum is attached to the bacterial cellbody by a complex structure consisting of ahook and a basal body. The hook is a short

curved structure that appears to act as theuniversal joint between the motor in the basalstructure and the flagellum.

Watch thiese movies:

http://www.youtube.com/watch?feature=endscreen&NR=1&v=BeLwGCJ0zdQ 339

http://www.youtube.com/watch?v=4hexn-DtSt4 54

http://www.websters-online-dictionary.org/definitions/Flagellum

Bacterial Structure
http://www.youtube.com/watch?feature=endscreen&NR=1&v=BeLwGCJ0zdQhttp://www.youtube.com/watch?v=4hexn-DtSt4http://www.websters-online-dictionary.org/definitions/Flagellumhttp://www.websters-online-dictionary.org/definitions/Flagellumhttp://www.websters-online-dictionary.org/definitions/Flagellumhttp://www.websters-online-dictionary.org/definitions/Flagellumhttp://www.websters-online-dictionary.org/definitions/Flagellumhttp://www.websters-online-dictionary.org/definitions/Flagellumhttp://www.youtube.com/watch?v=4hexn-DtSt4http://www.youtube.com/watch?v=4hexn-DtSt4http://www.youtube.com/watch?v=4hexn-DtSt4http://www.youtube.com/watch?feature=endscreen&NR=1&v=BeLwGCJ0zdQ


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B. Fimbriae (pili) are rigid proteinaceous surfaceappendages found in many gram negativebacteria. They are microfilaments extendingthrough the cell envelope and beyond.

They are shorter and finer than flagella; likeflagella, they are composed of structural proteinsubunits: pilins. Some pili contain a single typeof pilin, others more than one.

Minor proteins termed adhesinsare located at

the tips of pili and are responsible for theattachment properties.

Two classes can be distinguished: ordinary pili,which play a role in the adherence of symbioticand pathogenic bacteria to host cells, and sexpili, which are responsible for the attachment ofdonor and recipient cells in bacterial conjugation

Pili inhibit the phagocytic ability ofleukocytes.

Bacterial Structure


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Bacterial Structure

B. Fimbriae (pili)

Motility via pili is completely different from flagellar motion. Pilin molecules are arrangedhelically to form a straight cylinder that does not rotate and lacks a complete basal body.Their tips strongly adhere to surfaces at a distance from the cells. Pili then depolymerizefrom the inner end, thus retracting inside the cell. The result is that the bacterium moves inthe direction of the adhering tip. This kind of surface motility is called twitching and iswidespread among piliated bacteria.

The virulence of certain pathogenic bacteria depends on the production not only of toxinsbut also of"colonization antigens" which are ordinary pili that provide the cells withadherent properties.

Pili of different bacteria are antigenically distinct and elicit the formation ofantibodies by the host.Antibodies against the pili of one bacterial species will not preventthe attachment of another species.

Some bacteria, such as N gonorrhoeae, are able to make pili of different antigenic types(antigenic variation) and thus can still adhere to cells in the presence of antibodies to theiroriginal type of pili.

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Bacterial Structure

C. Envelope surfaceantigens are teichoic acidsor certain outer membraneproteins (OMPs) that affectadherence or virulence

(such as the ability toinvade nonphagocytic hostcells).

D. Capsules arepolysaccharides that inhibit

phagocytic uptake by avariety of mechanisms innon immune individuals.


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Bacterial Structure

INTERIOR STRUCTURES

A. Granules. Bacteria polymerize and store compounds (likephosphates) that are required in large amounts. This reduces theosmotic pressure on the bacterial cell and may result in granules inthe cells.

B. Lack of membrane-bound organelles. Bacteria are prokaryotic andlack membranebound organelles (e.g., mitochondria andlysosomes). Respiratory enzymes and cytochromes are embeddedin the cytoplasmic membrane.

C. Chromosomes. The bacterial chromosome is a single, covalentlyclosed circle of double-stranded DNA. There may be multiple copiesof the one chromosome.


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Bacterial Structure

D. Endospores.

Endospores occur in two Gram-positive genera of bacteria: Bacillus(aerobic) and Clostridium (anaerobic). The other bacteria known to formendospores are Thermoactinomyces, Sporolactobacillus, Sporosarcina,Sporotomaculum, Sporomusa, and Sporohalobacter.

Sporulation is triggered by neardepletion of any of several nutrients(carbon, nitrogen, or phosphorous). Each cell forms a single internalspore that is liberated when the mother cell undergoes autolysis.

The spore is a resting cell, highly resistant to boiling, cold, desiccationheat, and chemical agents (i. e. antiseptics); when returned to favorablenutritional conditions and activated (see below), the spore germinatesto produce a single vegetative cell.

Bacterial endospores


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Characteristic of Low G+C Gram + bacteria and by

far the most resistant endospores.

Triggered by stress as nutrient depravation or:

high temperature, high UV irradiation, desiccation,

chemical damage and enzymatic destruction.

It houses the cells DNA, ribosomes and large

amounts of dipicolinic acid.

http://micro.cornell.edu/cals/micro/research/labs/angert-lab/bacterialendo.cfm

Bacillus subtilis

-gram-negative bacteria
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Bacterial Morphology


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Bacteria differ from other single-cell microorganisms in boththeir cell structure and size, which varies from 0.3 5 m.Magnifications of 5001000x close to the resolution limits of

light microscopy are required to obtain useful images ofbacteria.

Bacteria have 4 majorshapes:

1) Cocci: spherical.

2) Bacilli: rods. Short bacilli are called coccobacilli.

3) Spiral forms: comma-shaped, S-shaped, or spiral-shaped.

4) Pleomorphic: lacking a distinct shape



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The different shaped

creatures organize

together into more

complex patterns, such

as pairs (diplococci),

clusters, strips, and

single bacteria with

flagella.


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Gram - PositiveThere are 6 classic gram-positive bacteria that cause disease inhumans, and basically every other organism is gram-negative.

Of the gram-positives, 2 are cocci, and the other 4 are rod-shaped

(bacilli).

The 2 gram-positive cocci both have the word coccus in their names:

1) Streptococcusforms strips of cocci.

2) Staphylococcusforms clusters of cocci.

Gram - Positive


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Two of the 4 gram-positive rods produce spores (spheres thatprotect a dormant bacterium from the harsh environment). Theyare:

3) Bac il lus

4) Clostr id ium

The last 2 gram-positive rods do not form spores:

5) Cory nebacterium

6) Lis teria, which surprisingly has endotoxin -surprising becauseallother organisms with endotoxin are gram-negative.

Gram - Negative


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Of the gram-negative organisms, there is only one group of gram-

negative cocci. It is actually a diplococcus: Neisseria.

There is also just 1 group of spiral-shaped organisms: the

Spirochetes. This group includes three genera:

1) Treponema,2) Bor relia, and

3) Leptospira

The rest are gram-negative rods or pleomorphic.

Exceptions


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1) Mycobacteriaare weakly gram-positive but stain better with a special staincalled the acid-fast stain. This special group includes organisms that causetuberculosis and leprosy.

2) Spirocheteshave a gram-negative cell wall but are too small to be seenwith the light microscope and so must be visualized with a special darkfieldmicroscope.

3) Mycoplasma do not have a cell wall. They only have a simple cell

membrane, so they are neither gram-positive nor gram-negative. They arethe tiniest free-living organisms capable of self replication. They lack apeptidoglycan cell wall and theur only protective layer is the cell membrane,which is packed with sterols.

4) Chlamydia and Rickettsiaare two groups of gram negative bacteria thatare obligate intracellular parasites. They need their hosts ATP as an energysource for their own cellular activity and use an ATP/ADP transloctor tosteal the ATP.


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Metabolic characteristics


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Bacteria can be divided into groups based on theirmetabolic properties. Two important properties include:

1) how the organism deals with oxygen, and

2) what the organism uses as a carbon and energy source.

Other properties include the different metabolic end-

products that bacteria produce such as gas.



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1. Oxygen

How bacteria deal with oxygen is a major factor in their classification. Molecularoxygen is very reactive, and when it snatches up electrons, it can formhydrogen peroxide (H2O2), superoxide radicals (O2-), and a hydroxyl radical(OH-). All of these are toxic unless broken down. In fact, our very ownmacrophages produce these oxygen radicals to pour over bacteria. Thereare 3 enzymes that some bacteria possess to break down these oxygen

products:

1) Catalase breaks down hydrogen peroxide in the following reaction:

2 H2O2 -+ 2 H2O + O2

2) Peroxidase also breaks down hydrogen peroxide.

3) Superoxide dismutase breaks down the superoxide radical in the followingreaction:

O2- + O2- + 2H+ -+ H2O2 + O2



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Bacteria are classified on a continuum. At one end are those that love oxygen,have all the preceding protective enzymes, and cannot live without oxygen. On

the opposite end are bacteria which have no enzymes and cannot live in thepresence of oxygen:

1) Obligate aerobes: These bacteria are just like us in that they use glycolysis, theKrebs TCA cycle, and the electron transport chain with oxygen as the finalelectron acceptor. They have all the mentioned enzymes.

2) Facultative anaerobes:Don't let this name fool you! These bacteria are aerob ic.They use oxygen as an electron acceptor in their electron transfer chain andhave catalase and superoxide dismutase. The only difference is that they cangrow in the absence of oxygen by using fermentat ionfor energy. Thus theyhave the faculty to be anaerobic but prefer aerobic conditions. This is similar tothe switch to anaerobic glycolysis that human muscle cells undergo duringsprinting. '

3) Microaerophilic bacteria (also called aerotolerant anaerobes): These bacteriause fermentation and have no electron transport system. They can tolerate lowamounts of oxygen because they have superoxide dismutase (but they have nocatalase).

4) Obligate anaerobes:These bacteria hate oxygen and have no enzymes todefend against it.

Metabolic characteristics: Oxygen Spectrum


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2. Carbon and Energy Source

Some organisms use light as an energy source (phototrophs), andsome use chemical compounds as an energy source(chemotrophs).

Of the organisms that use chemical sources, those that use inorganicsources, such as ammonium and sulfide, are called autotrophs.

Others use organic carbon sources and are heterotrophs.

All the medically important bacteria are chemoheterotrophs becausethey use chemical and organic compounds, such as glucose, forenergy.



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Fermentation (glycolysis)is used by many bacteria for oxygen

metabolism. In fermentation, glucose is broken down to pyruvic acid,yielding ATP directly.

There are different pathways for the breakdown of glucose to pyruvate,but the most common is the Embden-Meyerhof pathway(glycolysis).

Following fermentation the pyruvate must be broken down, and thedifferent end products formed in this process can be used to classifybacteria. Lactic acid, ethanol, propionic acid, butyric acid,acetone, and other mixed acids can be formed.



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Respiration is used with the aerobic and facultative anaerobicorganisms. Respiration includes glycolysis, Krebs tricarboxylic-acid cycle, and the electron transport chain coupled with

oxidative phosphorylation. These pathways combine to produceATP.

Obligate intracellular organisms are not capable of the metabolicpathways for ATP synthesis and thus must steal ATP from theirhost. These bacteria live in their host cell and cannot survive

without the host.

Further metabolic differences (such as sugar sources used, endproducts formed, and the specific need for certain nutrients) figure inclassifying bacteria and will be discussed in the sessions coveringspecific organisms.


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TheABCs of anaerobios are Actinomyces, Bacteroides and Clostridium.

Bacterial Growth


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BACTERIAL GROWTH is a coordinated process of increase in individual cell mass andsize, followed by duplication of the chromosome and cell division.

A. Since bacterial reproduction involves duplication of DNA without the addition ofoutside DNA, bacterial cell division is asexual and gives rise to geneticallyidentical cells. This process is called binary fission, because one cell alwaysgives rise to two cells.

B. Bacterial growth is measured by two basic methods:

1. Viable counts (colony counts) enumerate only those bacteria that can give rise to acolony. Viable methods give living cell number, not size.

2. Nonviable methods (e.g., optical density of the culture, dry cell mass, and quantitativemeasurement of an individual component); do not distinguish dead cells from livingcells.

C.A growth curve measures viable bacteria in a broth medium over time.

Bacterial Growth


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D. Not all bacterial species reproduce by binary fission.

A few bacterial species reproduce by budding; they form a small initialoutgrowth (a bud) that enlarges until its size approaches that of the

parent cell, and then it separates.

Some filamentous bacteria (certain actinomycetes) reproduce by

producing chains of conidiospores carried externally at the tips of thefilaments.

A few filamentous species simply fragment, and the fragments initiate

the growth of new cells.

Binary


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Bacteria normallyreproduce by binary fission.

The time required for a cell

to divide (and its population

To double) is called the

generation time. It varies

considerably among

organisms and with

environmental conditions,

such as temperature.

Most bacteria have a

generation time of1 to

3 hours; others require

more than 24 hours per

generation.

y

Fission


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Bacterial Growth


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If binary fission continues unchecked, an enormous number of cells

will be produced. If a doubling occurred every 20 minutes- which isthe case for E. coliunder favorable conditions- after 20 generations asingle initial cell would increase to over I million cells. This wouldrequire a little less than 7 hours. In 30 generations, or 10 hours, thepopulation would be I billion, and in 24 hours it would be a numbertrailed by 21 zeros.

It is difficult to graph population changes of such enormousmagnitude by using arithmetic numbers. This is why logarithmicscales are generall y used to graph bacterial growth.

Bacterial Growth


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Bacterial Growth

Visual representation

of increase in

bacterial number over

five generations.

Conversion of the

number of cells in a

poputation into thelogarithmic

expression of this

number.

Bacterial Growth


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In five generations (2*5), there wouldbe 32 cells; in ten generations (2*10),there would be 1024 cells, and so on.

Notice that the arithmetically plottedline (solid) does not clearly show the

population changes in the earlystages of the growth curve at thisscale.

The log 10 of the population isplotted at 5, 10, 15, and 20generations (dashed line). Notice that

a straight line is formed. This figuredemonstrates why it is necessary tograph changes in the immensenumbers of bacterial populations bylogarithmic plots rather than byarithmetic numbers, although at thecost of distorting our "commonperception of the actual situation.

To illustrate the difference between logarithmic and arithmetic graphing of

bacterial populations, let's express 20 bacterial generations both

logarithmically and arithmetically.

Bacterial Growth


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Bacterial Growth

There are four basic phases of growth:

Lag phase. This period of little or no cell division is called the lag phase, and it canlast for 1 hour or several days. During th is time, however, the cells are not dormant.The microbial population is undergoing a period of intense metabolic activityinvolving, in particular, synthesis of enzymes and various molecules.

Log phase. Eventually, the cells begin to divide and enter a period of growth, or

logarithmic increase, called the log phase, or exponential growth phase. Cellularreproduction is most active during this period, and generation time reaches aconstant minimum. Because the generation time is constant, a logarithmic plot ofgrowth during the log phase is a straight line.

Stationary phase. Eventually, the growth rate slows, the number of microbial deathsbalances the number of new cells, and the population stabilizes. What causes

exponential growth to stop is not always clear. The exhaustion of nutrients,accumulation of waste products, and harmful changes in pH may all playa role.

Death phase. The number of deaths eventually exceeds the number of new cellsformed, and the population enters the death phase, or logarithmic decline phase.This phase continues until the population is diminished to a tiny fraction of thenumber of cells in the previous phase or until the population dies out entirely.


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Growth Limitation by Environmental Factors


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Liebigs law of the minimum states that the total biomass of anorganism will be determined by the nutrient present in the lowestconcentration relative to the organisms requirements. This lawapplies in both the laboratory and in terrestrial and aquaticenvironments. An increase in a limiting essential nutrient such asphosphate will result in an increase in the microbial population untilsome other nutrient becomes limiting. If a specific nutrient is limiting,changes in other nutrients will have no effect.

Shelfords law of tolerance states that there are limits toenvironmental factors below and above which a microorganism

cannot survive and grow, regardless of the nutrient supply. Thiscan readily be seen for temperature. Each microorganism has a specifictemperature range in which it can grow. The same rule applies to otherfactors such as pH, light, salinity, oxygen level, and hydrostatic pressurein the marine environment.

Growth Limitation by


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y

Temperature

Microorganisms can be placed in different classes based on their

temperature ranges for growth. They are ranked in order of increasing

growth temperature range as psychrophiles, psychrotrophs,

mesophiles, thermophiles, and hyperthermophiles. Representative

ranges and optima for these five types are illustrated here.


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Bacterial Growth

Problem

A broth is inoculated to 2x10*2 cells/ml. If the lag phase is 20 minutes andthe generation time is 10 minutes, how many cells are there at the endof 60 minutes?

Bacterial GeneticsTh b t i l h i d bl t d d DNA l l th t i


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The bacterial chromosome is a double-stranded DNA molecule that isclosed in a giant loop. Because there is only one copy of this molecule percell, bacteria exist in a haploid state. Bacteria do not have nuclearmembranes surrounding their DNA.

Procaryotes do not engage in sexual union with other bacteria. Theyundergo gene replication, forming an exact copy of their genome, and thensplit in two, taking a copy with each half (binary fission).

We will briefly review the mechanisms of bacterial exchange of geneticinformation.

The exchange of genetic material allows for the sharing of genes that codefor proteins, such as those that provide antibiotic resistance, exotoxins,enzymes, and other virulence factors (pili, flagella, and capsules)CHANGE = SURVIVAL

Bacterial Genetics


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There are 4 ways in which bacteria are able to

exchange genetic fragments:

1) Transformation,

2) Transduction,3) Conjugation, and

4) Transposon insertion

Bacterial Genetics


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TRANSFORMATION

Naked DNA fragments from one bacterium, released during cell lysis,bind to the cell wall of another bacterium.

The recipient bacterium must be competent, which means that it hasstructures on its cell wall that can bind the DNA and take it upintracellularly.

Recipient competent bacteria are usually of the same speciesas thedonor.

The DNA that has been brought in can then incorporate itself into therecipient's genome if there is enough homology between strands(another reason why this transfer can only occur between closelyrelated bacteria).

Bacterial Genetics


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The famous example of this type of exchange is the experimentconducted by Frederick Griffith in 1928. He used the Streptococcuspneumoniae bacteria, which are classified into many different typesbased on differences in their cellular capsule.

Griffith used encapsulated pneumococci, which cause violent infectionand death in mice, and nonencapsulated pneumococci, which do not killmice.

Griffith heat-killed the smooth encapsulated bad guys and injectedthem, along with the live rough nonencapsulated pushovers, into mice.

The mice died, and when he cultured out bacteria from the blood, hecould only find live smooth encapsulated pneumococci.

The gene encoding the capsule had been released from the heat-killedbacteria and became incorporated into the living roughnonencapsulated bacteria. The rough bacteria were thus t ransformedinto virulent encapsulated smooth bacteria.

B t i l G ti


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Bacterial Genetics

Transduction occurs when a virus thatinfects bacteria, called abacteriophage, carries a piece ofbacterial DNA from one bacterium toanother.

Bacteriophages resemble most viruses

in having a protein coat called a capsidthat surrounds a molecule of DNA orRNA.

The phage will bind by its tail fibers tospecific receptors on the bacterial cellsurface. This is called adsorption.

The phage pushes the long hollowtube under its neck sheath through thebacterial cell wall and cytoplasmicmembrane. DNA in the head isinjected through the tube into thebacterium.


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Bacterial Genetics

Following adsorption and penetration, the injectedDNA takes over the host bacteria's RNApolymerasefor the transcription of phage DNA tomRNA..

New capsids, DNA, and enzymes are formed, andthe bacterial cell fills with new phages.

At some point the cell can hold no more particlesand lyses, releasing the phages.

To make things more complicated, there are twotypes of phages, virulent phages and temperatephages.

Virulent phages infect the bacteria, reproducing,and then lysing and killing the bacteria.

B t i l G ti


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Bacterial Genetics On the other hand, temperate phages do not

immediately lyse the bacteria they infect. Thetemperate phage undergoes adsorption andpenetration like the virulent phage but then, ratherthan undergoing transcription, its DNA becomesincorporated into the bacterial chromosome.The DNA then waits for a command to activate.

The integrated temperate phage genome is

called aprophage. Bacteria that have aprophage integrated into their chromosomeare calledlysogenic because at some time therepressed prophage can become activated. Onceactivated, the prophage initiates the production ofnew phages, beginning a cycle that ends withbacterial cell lysis. So temperate phages are likelittle genetic time bombs.

Lysogenic immunity is the term used to describethe ability of an integrated bacteriophage(prophage) to block a subsequent infection by asimilar phage. The first temperate phage to infecta bacteria produces a repressor protein. Thisadaptation ensures that the first temperate phageis the bacteria's sole occupant.

Bacterial GeneticsJust as there are two types of phages, there are two types of transduction.


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1. Virulent phages are involved in generalized transduction, and

2. Temperate phages in specialized transduction.

Specialized

Generalized

B t i l G ti


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Bacterial Genetics

Generalized transduction

After phage penetration into a host bacterium, the phage DNAis transcribed, replicated, and translated into capsids andenzymes. At this same time the bacterial DNA is repressedand eventually destroyed.

Sometimes pieces of the bacterial DNA are left intact. Ifthese pieces are the same size as the phage DNA, theycan accidentally be packed into the phage capsid head.

Following lysis of the cell and release of the phages, the onephage with bacterial DNA in its head can then infect anotherbacterium. It will inject the piece of bacterial DNA that it is"accidentally" carrying.

If there is some homology between the newly injectedstrand and the recipient bacterial genome, the piece maybecome incorporated. The gene on that piece could encodea protein that the recipient did not originally have, such as aprotein that inactivates an antibiotic.

In generalized transduction, the bacteriophage is onlycarrying bacterial DNA, so the recipient cell will survive.

This type of genetic transfer is more effective thantransformation because the transferred DNA piece isprotected from destruction during transfer by the phage capsidthat holds it.

Bacterial Genetics


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Bacterial Genetics

Generalized Transduction

A) Adsorption and penetration occur.The viral DNA is drawn as a thinline, and the bacterial circular DNAis drawn as a thick circle.

B) Destruction of the bacterial DNAleaves some intact (thick) pieces.The phage DNA has undergonereplication.

C) Capsids are translated and packed.The middle one has been packed

with a bacterial DNA fragment.D) Cell lysis occurs, liberating phages

including the phage with bacterialDNA.

Bacterial Genetics


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It occurs with temperate phages.The temperate phage penetrates, and then its DNAbecomes incorporated into the bacterial chromosome. It is then called a prophage,and the bacterium is now lysogenic.

When the prophage becomes active, its DNA is spliced out of the bacterialchromosome and is then replicated, translated, and packaged into a capsid.

If there is an error in splicing, a piece of bacterial DNA that lies at one side of theprophage will be cut, replicated, and packaged with the phage DNA. This result in atransfer of that piece of bacterial DNA to another bacteria (lysogenic conversion).

Specialized

transduction

B t i l G ti


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Bacterial Genetics

In conjugation DNA is transferred directly bycell-to-cell contact, resulting in an extremelyefficient exchange of genetic information.The exchange can occur between unrelatedbacteria and is the major mechanism fortransfer of antibiotic resistance.

For conjugation to occur, one bacterium

must have a self-transmissible plasmid, alsocalled an F plasmid (for fertility).Plasmidsare circular double-stranded DNAmolecules that lie outside thechromosome and can carry many genes,including thos

01 general microbiology

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