Bacterial AnatomyBacterial AnatomyRashmi.SRashmi.S

Anatomy of a Bacterial Cell

DescriptionDescription Bacteria are Prokaryotic, Bacteria are Prokaryotic,

unicellular that do not contain unicellular that do not contain chlorophyll.chlorophyll.

Size of bacteria may range from Size of bacteria may range from 0.2-1.5 micrometer in diameter 0.2-1.5 micrometer in diameter and 3-5 micrometer in lengthand 3-5 micrometer in length

DIFFERENCES BETWEEN PROKARYOTES AND DIFFERENCES BETWEEN PROKARYOTES AND EUKARYOTESEUKARYOTES

CharacterCharacter Prokaryotes Eukaryotes Prokaryotes Eukaryotes Nucleus:Nucleus:Nuclear MembraneNuclear Membrane Absent Absent Present Present Nucleolus AbsentNucleolus Absent Present Present Mitotic Division AbsentMitotic Division Absent PresentPresent

CytoplasmCytoplasmCytoplasmic Streaming AbsentCytoplasmic Streaming Absent PresentPresentPinocytosis Absent Pinocytosis Absent Present Present Lysosomes Absent Lysosomes Absent Present Present Golgi Apparatus AbsentGolgi Apparatus Absent PresentPresentEndoplasmic Reticulum AbsentEndoplasmic Reticulum Absent PresentPresentChemical CompositionChemical CompositionSterols AbsentSterols Absent PresentPresentMuramic Acid PresentMuramic Acid Present AbsentAbsentTeichoic Acid PresentTeichoic Acid Present AbsentAbsent

Classification of Bacteria based Classification of Bacteria based on their Shapeon their Shape

CocciCocci BacilliBacilli VibrioVibrio SpirillaSpirilla SpirochetesSpirochetes ActinomycetesActinomycetes MycoplasmaMycoplasma

Cellular Arrangement Cellular Arrangement In Cocci,In Cocci, Diplococci: Cocci arranged in pairsDiplococci: Cocci arranged in pairs

Streptococci: Arranged in chainsStreptococci: Arranged in chains

Staphylococci: Arranged in grape like Staphylococci: Arranged in grape like clustersclusters

In Bacilli,In Bacilli, Coccobacilli: Oval shapedCoccobacilli: Oval shaped

Palisades : Parallel, attached at any Palisades : Parallel, attached at any one end of the cellone end of the cell

Streptobacilli: In chainsStreptobacilli: In chains

VibrioVibrio Spirilla

Actinomycetes Mycoplasma

Structure of a Bacterial CellStructure of a Bacterial Cell(Bacterial Anatomy)(Bacterial Anatomy)

Examination of a bacterial cell reveals Examination of a bacterial cell reveals components of structurescomponents of structures

Some external to cell wall Some external to cell wall

Others internal to cell wallOthers internal to cell wall

Anatomy of a Bacterial Cell

Demonstration of the cell Demonstration of the cell wallwall

PlasmolysisPlasmolysis MicrodissectionMicrodissection Specific AntibodiesSpecific Antibodies Differential StainingDifferential Staining Electron MicroscopeElectron Microscope

Structure of the cell wallStructure of the cell wall Bacterial Bacterial cell wallcell wall provides structural integrity provides structural integrity

to the cell. to the cell. The bacterial cell wall differs from that of all The bacterial cell wall differs from that of all

other organisms by the presence of other organisms by the presence of PeptidoglycanPeptidoglycan

Peptidoglycan (Mucopeptide) is composed of Peptidoglycan (Mucopeptide) is composed of alternating chains of ..alternating chains of ..

N -Acetyl Glucoseamine and N-Acetyl Muramic N -Acetyl Glucoseamine and N-Acetyl Muramic acid,acid, which is cross linked by which is cross linked by Peptide chainsPeptide chains

Structure of Peptidoglycan

PeptidoglycanPeptidoglycan is responsible for the is responsible for the rigidity of the bacterial cell wall and rigidity of the bacterial cell wall and for the determination of cell shapefor the determination of cell shape

Based on the Based on the composition of cell composition of cell wall & Stainingwall & Staining bacteria are bacteria are classified into “classified into “Gram positive”Gram positive” and and ““Gram Negative’Gram Negative’

Gram’s Staining

Gram Positive Cell wallGram Positive Cell wall

The The Gram positiveGram positive cell wall is cell wall is characterized by the presence of a characterized by the presence of a very thick very thick PeptidoglycanPeptidoglycan layer layer

20-80 nm thick20-80 nm thick Cell wall contains90% Peptidoglycan Cell wall contains90% Peptidoglycan

and 10%Teichoic acidand 10%Teichoic acid

Interwoven in the cell wall of gram-Interwoven in the cell wall of gram-positive are positive are Teichoic acidsTeichoic acids and and lipoteichoic acidslipoteichoic acids. .

Teichoic acids composed of polymers Teichoic acids composed of polymers of glycerol, phosphates, and the sugar of glycerol, phosphates, and the sugar alcohol- ribitol. alcohol- ribitol.

Teichoic acids constitute for the major Teichoic acids constitute for the major surface antigens.surface antigens.

Eg: In Eg: In Streptococcus pneumoniaeStreptococcus pneumoniae Teichoic acid bears the antigenic Teichoic acid bears the antigenic determinants called the “Forssman determinants called the “Forssman antigen”antigen”

Gram Negative Cell WallGram Negative Cell Wall Gram negative cell wall contains a thin Gram negative cell wall contains a thin

PeptidoglycanPeptidoglycan layer adjacent to the layer adjacent to the Cytoplasmic membraneCytoplasmic membrane, ,

In addition to the In addition to the PeptidoglycanPeptidoglycan layer, the layer, the Gram negative cell wall also contains an Gram negative cell wall also contains an additional outer membrane composed by additional outer membrane composed by PhospholipidsPhospholipids and Lipopolysaccharide and Lipopolysaccharide which face into the external environment. which face into the external environment.

The LPS present on the Gm negative The LPS present on the Gm negative cell wall consists of 3 regions:cell wall consists of 3 regions:

Polysaccharide determining O antigenPolysaccharide determining O antigen Core PolysaccharideCore Polysaccharide Glycolipid portion /Lipid AGlycolipid portion /Lipid A

All the three factors are responsible All the three factors are responsible for the endotoxic activities………for the endotoxic activities………

LPS Endotoxin causes a form of Septic LPS Endotoxin causes a form of Septic Shock for which there is no direct Shock for which there is no direct treatmenttreatment

Cytoplasmic MembraneCytoplasmic Membrane It is a thin layer lining the inner It is a thin layer lining the inner

surface of the cell wall.surface of the cell wall.

Semipermiable membrane controlling Semipermiable membrane controlling the flow of metabolitesthe flow of metabolites

Chemically ,consists of Lipoprotein Chemically ,consists of Lipoprotein and carbohydrates. Sterols are absentand carbohydrates. Sterols are absent

CytoplasmCytoplasm Colloidal system of variety of organic Colloidal system of variety of organic

and inorganic solutes in Viscous and inorganic solutes in Viscous watery solutionwatery solution

No ER,& MitochondriaNo ER,& Mitochondria

Contains Mesosomes Inclusions and Contains Mesosomes Inclusions and VacuolesVacuoles

MesosomesMesosomes Vesicular, convoluted invaginations of Vesicular, convoluted invaginations of

the plasma membranethe plasma membrane Prominent in GM+ bacteriaProminent in GM+ bacteria Principal sites of Respiratory enzymesPrincipal sites of Respiratory enzymes Analogous to mitochondria in Analogous to mitochondria in

EukaryotesEukaryotes

NucleusNucleus Bacterial nuclei “Bacterial nuclei “have no nuclear have no nuclear

membranemembrane “ “or the nucleolus.or the nucleolus. Genome consists of a single double Genome consists of a single double

stranded DNA.stranded DNA. Might be a Circular form or may be Might be a Circular form or may be

open under certain condition to form open under certain condition to form a long chain.a long chain.

PlasmidsPlasmids Extra chromosomal DNAExtra chromosomal DNA

Circular capable of autonomous Circular capable of autonomous replication.replication.

Transferred from one bacterium to Transferred from one bacterium to another .another .

ImportanceImportanceTheir presence confers Their presence confers

certain special characters……certain special characters……ToxigenicityToxigenicityAntibiotic ResistanceAntibiotic ResistanceAbility to use certain unusual Ability to use certain unusual

components as nutrientscomponents as nutrients

Structures external to Structures external to BacteriaBacteria

CapsuleCapsule

FlagellaFlagella

Pili(Fimbriae)Pili(Fimbriae)

CapsuleCapsule

Viscid material secreted by bacteria Viscid material secreted by bacteria around the cell surfacearound the cell surface

CapsuleCapsule is a sharply defined, organized is a sharply defined, organized structure (structure (Eg: Eg: PneumococcusPneumococcus))

Loose undemarkated structure as in Loose undemarkated structure as in Lueconostoc Lueconostoc is a is a Slime layer.Slime layer.

Colorless capsule surrounding the bacterial cell

Capsular Staining

Most bacterial capsules are composed Most bacterial capsules are composed of Polysaccharidesof Polysaccharides

Eg: Eg: Klebsiella pneumoniaeKlebsiella pneumoniae

A few capsules are PolypeptidesA few capsules are PolypeptidesEg: Eg: Bacillus anthracisBacillus anthracis

Quellung ReactionQuellung Reaction Described by Described by Neufeld(1902).Neufeld(1902). Serological method of demonstrating the Serological method of demonstrating the

capsule.capsule. Suspension of capsulated bacterium is Suspension of capsulated bacterium is

mixed with its specific anticapsular mixed with its specific anticapsular serum & examined under the microscope serum & examined under the microscope ,capsule appears prominent & swollen.,capsule appears prominent & swollen.

Used to type Used to type Pneumococci.Pneumococci.

Functions of CapsulesFunctions of Capsules Antiphagocytic,thus contribute Antiphagocytic,thus contribute

“Virulence”.“Virulence”. Protects against “Lysozyme”Protects against “Lysozyme” Promote attachment of bacteria to Promote attachment of bacteria to

surface(Eg: surface(Eg: StreptococcusStreptococcus mutansmutans).). Permits bacteria to adhere to Permits bacteria to adhere to

Medical Implants & Catheters.Medical Implants & Catheters.

Toxicity to host cell – Eg: Toxicity to host cell – Eg: BacteroidesBacteroides fragilis.fragilis.

Provide protection against Provide protection against temporary drying.temporary drying.

Block the attachment Block the attachment ofBacteriophagesofBacteriophages..

Applications:Applications:

Used in serological typingUsed in serological typing

Detection of capsule in Blood, CSF Detection of capsule in Blood, CSF provides a rapid method of diagnosisprovides a rapid method of diagnosis

Used in preparation of vaccinesUsed in preparation of vaccinesEg: H.influenzaeEg: H.influenzae

FlagellaFlagella

Unbranched, long ,filaments ,made up Unbranched, long ,filaments ,made up of protein “of protein “FlagellinFlagellin””

Organs of locomotionOrgans of locomotion

Found in all motile bacteria except Found in all motile bacteria except SpirochetesSpirochetes

Flagella are highly antigenic,Flagella are highly antigenic,

Termed as the Termed as the ‘H’ Antigen‘H’ Antigen..

Some of the immune responses are Some of the immune responses are directed against these proteins.directed against these proteins.

StructureStructure 3-20 Micrometer.3-20 Micrometer.

Each flagellum consists of 3 partsEach flagellum consists of 3 parts 1.Filament 1.Filament 2.Hook2.Hook 3.Basal body3.Basal body

Flagellar Arrangement

Kinds of MotilityKinds of Motility:: Darting motilityDarting motility : : V.choleraeV.cholerae Tumbling motilityTumbling motility::

L.monocyctogenesL.monocyctogenes Cork &screw motilityCork &screw motility:: T.pallidumT.pallidum Stately motile Stately motile : : Clostridium Clostridium

spp.spp. Serpentine motilitySerpentine motility: : Salmonella Salmonella

(Except S.gallonarum pullorum)(Except S.gallonarum pullorum)

Detection of motility :Detection of motility :

Direct observation by hanging Direct observation by hanging dropdrop

Dark field microscopyDark field microscopyMotility mediaMotility media

Flagellar stainingFlagellar staining

Electron microscopyElectron microscopy

Immunological detection Immunological detection of “H” antigenof “H” antigen

FimbriaeFimbriae

Hair like surface appendagesHair like surface appendages

0.5-10 nm thick0.5-10 nm thick

Shorter thinner than flagellaShorter thinner than flagella

Formed of protein subunits – PilinFormed of protein subunits – Pilin

FunctionsFunctions Organs of adhesionOrgans of adhesion Forms “Pellicles”Forms “Pellicles” Hemagglutination –Clumping of RBC’s Hemagglutination –Clumping of RBC’s

((EscherichiaEscherichia,,KlebsiellaKlebsiella)) Special type of Fimbriae called Sex Special type of Fimbriae called Sex

pili,help in attachment to other pili,help in attachment to other bacteriabacteria

EndosporesEndospores Highly resistant stages of bacteriaHighly resistant stages of bacteria

Spores germinate to form a single Spores germinate to form a single Vegitative cell.Vegitative cell.

It is formed inside the cell .It is formed inside the cell .

Eg: Eg: BacillusBacillus, , ClostridiumClostridium

Endospore

Core contains the Nuclear bodyCore contains the Nuclear bodySurrounded by a Spore Wall.Surrounded by a Spore Wall.Outside this is a thick Spore Outside this is a thick Spore

cortexcortexThis is covered in turn by a This is covered in turn by a

tough Spore coat.tough Spore coat.Exosporium is additional outer Exosporium is additional outer

covering, which exhibits ridges covering, which exhibits ridges and groovesand grooves

Factor responsible for the resistance Factor responsible for the resistance of sporesof spores

Presence of calcium dipicolinic acidPresence of calcium dipicolinic acid

Endospore inside bacteria

Position of SporesA = oval, terminal; B = rectangular, terminal; C = rectangular, sub

terminal,D = rectangular, central; E = circular, terminal; F = circular, central; G = terminal, club-shaped.

Pleomorphism and Involution Pleomorphism and Involution formsforms

Process of exhibiting variation in the shape Process of exhibiting variation in the shape and size of individual cells – Pleomorphismand size of individual cells – Pleomorphism

Eg: H.influenzaeEg: H.influenzae Certain bacteria exhibit swollen and Certain bacteria exhibit swollen and

aberrant forms in ageing cultures – aberrant forms in ageing cultures – Involution formsInvolution forms

This may be due to defective cell wall This may be due to defective cell wall synthesis or due to Autolytic Enzymessynthesis or due to Autolytic Enzymes

Eg: Eg: Yersinia, GonococcusYersinia, Gonococcus

Protoplasts,Spheroplasts and Protoplasts,Spheroplasts and L-FormsL-Forms

Removal of bacterial cell wall by Removal of bacterial cell wall by hydrolysis with Lysozyme or hydrolysis with Lysozyme or antibiotics like Penicillin, liberates ..antibiotics like Penicillin, liberates ..

““Protoplasts” from Gram positive cellsProtoplasts” from Gram positive cells ““Spheroplasts” from Gram negative Spheroplasts” from Gram negative

cellcell(retain the outer membrane and PG.)(retain the outer membrane and PG.)

When Protoplasts and Spheroplasts When Protoplasts and Spheroplasts are able to grow and divide they are are able to grow and divide they are called the called the L-Forms.L-Forms.

First observed by Kleineberger-NobelFirst observed by Kleineberger-Nobel Named it as L forms after Lister Named it as L forms after Lister

Institute London.Institute London.Eg: Streptobacillus moniliformisEg: Streptobacillus moniliformis

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