0 general 1 bacterial structure long (1)

8/10/2019 0 General 1 Bacterial Structure Long (1)

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BatterjeeMedical College


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Ass. Prof . Dr. Manal El Said

Head of M icrobiology Department

Bacterial Introduction

and Structure


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What is

Microbiology


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Medical microbiology deals with the study of

microorganisms which are of medical importance and

causing diseases in human beings.

Microbiology

Microbiology is the study of microorganisms, which aremicroscopic, unicellular, and cell-cluster organisms.


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TaxonomicRank Bacteria were first observed by Antonie van

Leeuwenhoek in 1676, using a single-lensmicroscope of his own design.

He called them "animalcules" and published his

observations in the Royal Society.

The name "bacterium" was introduced later, by

Christian Gottfried Ehrenbergin 1838.
http://en.wikipedia.org/wiki/File:Biological_classification_L_Pengo_vflip.svghttp://en.wikipedia.org/wiki/File:Biological_classification_L_Pengo_vflip.svg


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Comparison of Medically

Important OrganismsCharacteristic Viruses Bacteria Fungi Protozoa and

Helminths

Cells No Yes Yes Yes

Approximate

diameter (m)

0.020.2 15 310 (yeasts) 1525

(trophozoites)

Nucleic acid Either DNA or

RNA

Both DNA and

RNA

Both DNA and

RNA

Both DNA and

RNA

Type of

nucleus

None Prokaryotic Eukaryotic Eukaryotic

Ribosomes Absent 70S 80S 80S

Mitochondria Absent Absent Present PresentNature of outer

surface

Protein capsid

and lipoprotein

envelope

Rigid wall

containing

peptidoglycan

Rigid wall

containing

chitin

Flexible

membrane

Motility None Some None Most

Method ofreplication

Not binaryfission

Binary fission Budding ormitosis

Mitosis


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Eukaryotes & Prokaryotes

Characteristic Prokaryotic Bacterial Cells Eukaryotic

DNA within a nuclear membrane No YesMitotic division No Yes

DNA associated with histones No Yes

Chromosome number One More than one

Membrane-bound organelles, such

as mitochondria and lysosomes

No Yes

Size of ribosome 70S 8OS

Cell wall containing peptidoglycan Yes No

Cells have evolved into two types:

- Eukaryotic

- Prokaryotic

Histonesare highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into

structural units called nucleosomes.[They are the chief protein components of chromatin, acting asspools around which DNA winds, and play a role in gene regulation


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Structure of

Bacterial Cells


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Structure of Bacterial Cells (1)

Bacteria are classified by shape

into three basic groups:

- Cocci: round

- Bacilli: rods- Spirochetes:spiral

Pleomorphic (many-shaped)

bacteria: are variable in shape

The shape of a bacterium is

determined by its rigid cell wall.

The microscopic appearance of a

bacterium is important criteria

used in its identification.

Shape &Size (1)


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Shape &Size (2)

Structure of Bacterial Cells(2)


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The arrangement of bacteria is important:

- Cocci in pairs (diplococci)

in chains (streptococci)

in grapelike clusters (staphylococci).

These arrangements are determined by the orientation and

degree of attachment of the bacteria at the time of cell division.

Bacteria range in size from about 0.2 to 5 m.

The Mycoplasma(smallest bacteria) are :

- About the same size as the largest viruses (poxviruses)

- The smallest organisms exist outside a host.

Bo rrel ia,are as long as 10 m, i.e., they are longer than a

human red blood cell, which is 7 m in diameter.


Shape &Size (3)


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Structure (1)Structure Chemical Composition Function

Essential components

Cell wall

Peptidoglycan Sugar (glycan)backbone with

cross-linked peptide

side chains

1.Gives rigid support2.Protects against osmotic pressure

3.Site of action of penicillins &

cephalosporins (they inhibit the

transpeptidase that makes the cross-

links between two adjacent tetrapeptides)

4.Degraded by lysozyme

N.B. lysozyme:

-They are enzymes present in human

tears, mucus, & saliva.

-They cleave the peptidoglycan backboneby breaking its glycosyl bonds.


B j M di l C ll


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Structure (2)Structure Chemical Composition Function


Outer membrane of

gram-negative bacteria

Lipid A Toxic component of endotoxin

Polysaccharide Major surface antigen used in

laboratory diagnosis

Surface fibers of gram-

positive bacteria

Teichoic acid Major surface antigen but rarely

used in laboratory diagnosis

Plasma membrane Lipoprotein bilayerwithout sterols

1. Active transport of moleculesinto the cell

2. Energy generation by

oxidative phosphorylation,

3. Synthesis of precursors of the

cell wall4. Secretion of enzymes & toxins


B tt j M di l C ll


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Comparison of Cell Walls of Gram-Positive and Gram-Negative Bacteria

Component Gram-Positive Gram-Negative

Peptidoglycan Thicker; multilayer Thinner; single layer

Teichoic acidsfibers protrude outside the

peptidoglycan

- Induce septic shock

- Mediate the attachment of staphylococci

to mucosal cells.

Yes No

Periplasmic space:

-Lying between the outer membrane layer

and the cytoplasmic membrane

-The site, of enzymes -lactamases thatdegrade penicillins and -lactam drugs.

No Yes

Lipopolysaccharide (endotoxin)

Complex outer layer consisting of:

-liopolysaccharide

-lipoprotein,

-phospholipid

No Yes



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B tt j M di l C ll


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Gram stain: Gram-Positive and Gram-Negative Bacteria


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Batterjee Medical College


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Nucleoid DNA

- It is single, circular molecule.-It has a molecular weight of 2

x 109.

-It contains about 2000 genes.

Genetic material

It is the area of the cytoplasm in

which DNA is located.

Bacterial DNA has no introns,

whereas eukaryotic DNA does.

The nucleoid contains : Nonuclear membrane.

Nonucleolus.

No mitotic spindle.

NoHistones.

Structure (3)


Structure Chemical Composition Function




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Ribosome RNA and protein in 50S and 30S

subunits

Protein synthesis.

Site of action of:- Aminoglycosides

- Erythromycin

- Tetracyclines

- Chloramphenicol

Mesosome Invagination of plasma membrane Participates in cell division

Periplasm Space between plasma

membrane and outer membrane

Contains many hydrolytic

enzymes & -lactamases

Structure (4)






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Nonessential components

Plasmid Plasmids are DNA molecules:

- Extrachromosomal

- Double-stranded

- Circular

- Replicating independently

of the bacterial chromosome

and can be integrated into it.

- It occur in gram-positive and

gram-negative bacteria.

Plasmids carry the genes :

1- Antibiotic resistance

2- Resistance to heavy metals

3- Resistance to ultraviolet light

4- Pili (fimbriae)

5- Exotoxins, including enterotoxins

Structure (5)




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Plasmid Types of Plasmids:

Transmissible plasmids

-They transferred from cell

to cell by conjugation

-They are large (MW 40100

million)

-They are present in a few

(13) copies per cell.Nontransmissible plasmids

-They do not contain thetransfer genes

-They are small (MW 320

million)

-They are present in many(1060) copies per cell.

Other plasmid-encoded products are :

- Bacteriocins are toxic proteinsproduced by certain bacteria that are

lethal for other bacteria.

- Nitrogen fixationenzymes.

- Antibioticsproduced by Streptomyces

- Degradative enzymes produced by

Pseudomonas

Structure (6)

Structure of Bacterial Cells



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Transposons

(Jumping

Genes)

Transposons are pieces of

DNA that move from one site

to another either within or

between the DNA, plasmids,

& bacteriophages.

They are not capable of

independent replication.

They replicate as part of the

DNA in which they are

integrated.

More than one transposon

can be located in the DNA

Types of transposons:

1-Replicative transposition

They move by replicating their

DNA and inserting the new copy

into another site

2-Direct transposition

They are excised from the site

without replicating and then

inserted into the new site .

Transposons code for:

Drug-resistant enzymes

Toxins or metabolic enzymes

Mutations in the gene into which

they insert .Alter expression of nearby genes.

Structure (7)




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Transposons

(Jumping

Genes)

They have four domains

First domain:On each end is a short DNA

sequence of inverted repeat

They are involved in theintegration of the transposon

into the recipient DNA.

Second domain

The gene for the transposase

It is the enzyme that mediates

the excision and integration

processes.

Third region

The gene for the repressor

It regulates the synthesis of

both the transposase &the gene

product of the fourth domain

Fourth domain

The gene product

It is an enzyme-mediating

antibiotic resistance.

Structure (8)




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j g



Insertion

sequences

They are a type of

transposon that has fewer

bases (8001500base pairs)

They can be found in

multiple copies at the ends

oflarger transposon units .

They can cause mutations at

their site of integration

Structure (9)




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Capsule It is a gelatinous layercovering

the bacterium.

It is composed of

polysaccharide (except

anthrax bacillus D-glutamic

acid).

The sugar components of the

polysaccharide determine the

serologic type within a

species.

It protects against phagocytosis.

Specific identification made by

using antiserum against the

capsular polysaccharide.

Capsular polysaccharides are

used as the antigensin vaccines

It may play a role in the

adherence of bacteria to human

tissues.

Structure(10)




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j g



Glycocalyx

Slime Layer

Polysaccharide It covers surfaces like a film and allows the

bacteria to adherefirmly to various

structures

It is an important component of biofilms

It mediates adherence of bacteria, such as

Streptococcus mutans,to the surface of

teeth.Granule Glycogen, lipids,

polyphosphates

Site of nutrients in cytoplasm

Volutin is a reserve of high energy stored

in the form of polymerized metaphosphate.

It appears as a "metachromatic" granule

since it stains redwith methylene blue dyeinstead of blue.

Structure (11)




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j g



Flagellum

mono,

amphi,

lopho,

amphilop

ho, peritrichous

They are long whiplike

appendages

Composed of many subunits of a

single protein, flagellin, arranged

in several intertwined chains.

Three types of arrangements:

1-Monotrichous:

Single polar flagellum

2-Lophotrichous

Multiple polar flagella

3- Peritrichous

Flagella distributed

over the entire cell

It moves the bacteria toward

nutrients and other attractants

a process called chemotaxis.

They are highly antigenic (H

antigens), and some of the

immune responses to

infection are directed against

these proteins.

NB: Spirochetes move by

using a flagellum like

structure called the axial

filament, which wraps around

the spiral-shaped cell toproduce an undulating motion

Structure (12)

Structure of Bacterial Cellsmono, amphi, lopho, amphilopho, peri--trichous
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Pilus or

fimbria Pili are hairlike filaments that

extend from the cell surface.

They are shorter and straighter

than flagella.

They are composed of subunitsof pilin, a proteinarranged in

helical strands.

They are found mainly on gram-

negative organisms.

Pili have two important roles:

1- Mediates attachmentto cell

surfaces.

2- Sex pilusmediates attachment

of two bacteria duringconjugation.

Structure (13)




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Spore It forms inside the cell & contains

- Bacterial DNA

- A small amount of cytoplasm

- Cell membrane

- Peptidoglycan

- Very little water

-A thick, keratinlike coat that isresponsible for the resistance of

the spore to heat, dehydration,

radiation &chemicals.

-This resistance mediated by

dipicolinic acid (calcium ion

chelator)

Spore formation (sporulation)

occurs when nutrients are depleted

& the spore ishighly resistant.

It has no metabolicactivity.

Upon exposure to water and the

appropriate nutrients:

-Specific enzymes degrade the coat

- Water and nutrients enter

- Germination into a bacterial cell.

Structure (14)




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Important Features of Spores Medical Implications

Highly resistant to heating; sporesare not killed by boiling (100C), butare killed at 121C.

Medical supplies must be heated to 121Cfor at least 15 minutes to be sterilized.

Highly resistant to many chemicals Use only solutions designated assporicidal

They can survive for many years,especially in the soil.

Wounds contaminated with soil can beinfected with spores.

They exhibit no measurablemetabolic activity.

Antibiotics are ineffective as they act byinhibiting metabolic pathways of bacteria& spore coat is impermeable to antibiotics.

Spores form when nutrients areinsufficient & germinate to formbacteria when nutrients available.

Spores are not often found at the site ofinfections because nutrients are notlimiting.

Spores are produced by Baci l lusand

Clostr id ium genera

Infections transmitted by spores are

caused by species of Baci l lus orClostr id ium.


Structure (15)



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