Bacterial Anatomy Rashmi.S

Anatomy of a Bacterial Cell

Description Bacteria are Prokaryotic, unicellular that do not contain chlorophyll. Bacteria are Prokaryotic, unicellular that do not contain chlorophyll. Size of bacteria may range from micrometer in diameter and 3-5 micrometer in length Size of bacteria may range from micrometer in diameter and 3-5 micrometer in length

DIFFERENCES BETWEEN PROKARYOTES AND EUKARYOTES Character Prokaryotes Eukaryotes Nucleus: Nuclear Membrane AbsentPresent Nucleolus AbsentPresent Mitotic Division AbsentPresent Cytoplasm Cytoplasmic Streaming AbsentPresent Pinocytosis Absent Present Lysosomes Absent Present Golgi Apparatus AbsentPresent Endoplasmic Reticulum AbsentPresent Chemical Composition Sterols AbsentPresent Muramic Acid PresentAbsent Teichoic Acid PresentAbsent

Classification of Bacteria based on their Shape Cocci Bacilli Vibrio Spirilla Spirochetes Actinomycetes Mycoplasma

Cellular Arrangement In Cocci, Diplococci: Cocci arranged in pairs Diplococci: Cocci arranged in pairs Streptococci: Arranged in chains Streptococci: Arranged in chains Staphylococci: Arranged in grape like clusters Staphylococci: Arranged in grape like clusters

In Bacilli, Coccobacilli: Oval shaped Coccobacilli: Oval shaped Palisades : Parallel, attached at any one end of the cell Palisades : Parallel, attached at any one end of the cell Streptobacilli: In chains Streptobacilli: In chains

VibrioSpirilla

Actinomycetes Mycoplasma

Structure of a Bacterial Cell (Bacterial Anatomy) Examination of a bacterial cell reveals components of structures Examination of a bacterial cell reveals components of structures Some external to cell wall Some external to cell wall Others internal to cell wall Others internal to cell wall

Anatomy of a Bacterial Cell

Demonstration of the cell wall Plasmolysis Plasmolysis Microdissection Microdissection Specific Antibodies Specific Antibodies Differential Staining Differential Staining Electron Microscope Electron Microscope

Structure of the cell wall Bacterial cell wall provides structural integrity to the cell. Bacterial cell wall provides structural integrity to the cell.cell wallcell wall The bacterial cell wall differs from that of all other organisms by the presence of Peptidoglycan The bacterial cell wall differs from that of all other organisms by the presence of Peptidoglycan Peptidoglycan Peptidoglycan (Mucopeptide) is composed of alternating chains of.. Peptidoglycan (Mucopeptide) is composed of alternating chains of.. N -Acetyl Glucoseamine and N-Acetyl Muramic acid, which is cross linked by Peptide chains N -Acetyl Glucoseamine and N-Acetyl Muramic acid, which is cross linked by Peptide chains

Structure of Peptidoglycan

Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape Peptidoglycan Based on the composition of cell wall & Staining bacteria are classified into “Gram positive” and “Gram Negative’ Based on the composition of cell wall & Staining bacteria are classified into “Gram positive” and “Gram Negative’

Gram’s Staining

Gram Positive Cell wall The Gram positive cell wall is characterized by the presence of a very thick Peptidoglycan layer The Gram positive cell wall is characterized by the presence of a very thick Peptidoglycan layerGram positive PeptidoglycanGram positive Peptidoglycan nm thick nm thick Cell wall contains90% Peptidoglycan and 10%Teichoic acid Cell wall contains90% Peptidoglycan and 10%Teichoic acid

Interwoven in the cell wall of gram- positive are Teichoic acids and lipoteichoic acids. Interwoven in the cell wall of gram- positive are Teichoic acids and lipoteichoic acids. Teichoic acids composed of polymers of glycerol, phosphates, and the sugar alcohol- ribitol. Teichoic acids composed of polymers of glycerol, phosphates, and the sugar alcohol- ribitol.

Teichoic acids constitute for the major surface antigens. Teichoic acids constitute for the major surface antigens. Eg: In Streptococcus pneumoniae Teichoic acid bears the antigenic determinants called the “Forssman antigen”

Gram Negative Cell Wall Gram negative cell wall contains a thin Peptidoglycan layer adjacent to the Cytoplasmic membrane, Gram negative cell wall contains a thin Peptidoglycan layer adjacent to the Cytoplasmic membrane, Peptidoglycan Cytoplasmic membrane Peptidoglycan Cytoplasmic membrane In addition to the Peptidoglycan layer, the Gram negative cell wall also contains an additional outer membrane composed by Phospholipids and Lipopolysaccharide which face into the external environment. In addition to the Peptidoglycan layer, the Gram negative cell wall also contains an additional outer membrane composed by Phospholipids and Lipopolysaccharide which face into the external environment.Peptidoglycan PhospholipidsPeptidoglycan Phospholipids

The LPS present on the Gm negative cell wall consists of 3 regions: Polysaccharide determining O antigen Polysaccharide determining O antigen Core Polysaccharide Core Polysaccharide Glycolipid portion /Lipid A Glycolipid portion /Lipid A

All the three factors are responsible for the endotoxic activities……… All the three factors are responsible for the endotoxic activities……… LPS Endotoxin causes a form of Septic Shock for which there is no direct treatment LPS Endotoxin causes a form of Septic Shock for which there is no direct treatment

Cytoplasmic Membrane It is a thin layer lining the inner surface of the cell wall. It is a thin layer lining the inner surface of the cell wall. Semipermiable membrane controlling the flow of metabolites Semipermiable membrane controlling the flow of metabolites Chemically,consists of Lipoprotein and carbohydrates. Sterols are absent Chemically,consists of Lipoprotein and carbohydrates. Sterols are absent

Cytoplasm Colloidal system of variety of organic and inorganic solutes in Viscous watery solution Colloidal system of variety of organic and inorganic solutes in Viscous watery solution No ER,& Mitochondria No ER,& Mitochondria Contains Mesosomes Inclusions and Vacuoles Contains Mesosomes Inclusions and Vacuoles

Mesosomes Vesicular, convoluted invaginations of the plasma membrane Vesicular, convoluted invaginations of the plasma membrane Prominent in GM+ bacteria Prominent in GM+ bacteria Principal sites of Respiratory enzymes Principal sites of Respiratory enzymes Analogous to mitochondria in Eukaryotes Analogous to mitochondria in Eukaryotes

Nucleus Bacterial nuclei “have no nuclear membrane “or the nucleolus. Bacterial nuclei “have no nuclear membrane “or the nucleolus. Genome consists of a single double stranded DNA. Genome consists of a single double stranded DNA. Might be a Circular form or may be open under certain condition to form a long chain. Might be a Circular form or may be open under certain condition to form a long chain.

Plasmids Extra chromosomal DNA Extra chromosomal DNA Circular capable of autonomous replication. Circular capable of autonomous replication. Transferred from one bacterium to another. Transferred from one bacterium to another.

Importance Their presence confers certain special characters…… Their presence confers certain special characters…… Toxigenicity Toxigenicity Antibiotic Resistance Antibiotic Resistance Ability to use certain unusual components as nutrients Ability to use certain unusual components as nutrients

Structures external to Bacteria Capsule Capsule Flagella Flagella Pili(Fimbriae) Pili(Fimbriae)

Capsule Viscid material secreted by bacteria around the cell surface Viscid material secreted by bacteria around the cell surface Capsule is a sharply defined, organized structure (Eg: Pneumococcus) Capsule is a sharply defined, organized structure (Eg: Pneumococcus) Loose undemarkated structure as in Lueconostoc is a Slime layer. Loose undemarkated structure as in Lueconostoc is a Slime layer.

Colorless capsule surrounding the bacterial cell

Capsular Staining

Most bacterial capsules are composed of Polysaccharides Most bacterial capsules are composed of Polysaccharides Eg: Klebsiella pneumoniae A few capsules are Polypeptides A few capsules are Polypeptides Eg: Bacillus anthracis

Quellung Reaction Described by Neufeld(1902). Described by Neufeld(1902). Serological method of demonstrating the capsule. Serological method of demonstrating the capsule. Suspension of capsulated bacterium is mixed with its specific anticapsular serum & examined under the microscope,capsule appears prominent & swollen. Suspension of capsulated bacterium is mixed with its specific anticapsular serum & examined under the microscope,capsule appears prominent & swollen. Used to type Pneumococci. Used to type Pneumococci.

Functions of Capsules Antiphagocytic,thus contribute “Virulence”. Antiphagocytic,thus contribute “Virulence”. Protects against “Lysozyme” Protects against “Lysozyme” Promote attachment of bacteria to surface(Eg: Streptococcus mutans). Promote attachment of bacteria to surface(Eg: Streptococcus mutans). Permits bacteria to adhere to Medical Implants & Catheters. Permits bacteria to adhere to Medical Implants & Catheters.

Toxicity to host cell – Eg: Bacteroides fragilis. Toxicity to host cell – Eg: Bacteroides fragilis. Provide protection against temporary drying. Provide protection against temporary drying. Block the attachment ofBacteriophages. Block the attachment ofBacteriophages.

Applications: Used in serological typing Used in serological typing Detection of capsule in Blood, CSF provides a rapid method of diagnosis Detection of capsule in Blood, CSF provides a rapid method of diagnosis Used in preparation of vaccines Used in preparation of vaccines Eg: H.influenzae

Flagella Unbranched, long,filaments,made up of protein “Flagellin” Unbranched, long,filaments,made up of protein “Flagellin” Organs of locomotion Organs of locomotion Found in all motile bacteria except Spirochetes Found in all motile bacteria except Spirochetes

Flagella are highly antigenic, Flagella are highly antigenic, Termed as the ‘H’ Antigen. Termed as the ‘H’ Antigen. Some of the immune responses are directed against these proteins. Some of the immune responses are directed against these proteins.

Structure 3-20 Micrometer Micrometer. Each flagellum consists of 3 parts Each flagellum consists of 3 parts 1.Filament 1.Filament 2.Hook 2.Hook 3.Basal body 3.Basal body

Flagellar Arrangement

Kinds of Motility : Darting motility :V.cholerae Darting motility :V.cholerae Tumbling motility:L.monocyctogenes Tumbling motility:L.monocyctogenes Cork &screw motility:T.pallidum Cork &screw motility:T.pallidum Stately motile : Clostridium spp. Stately motile : Clostridium spp. Serpentine motility: Salmonella (Except S.gallonarum pullorum) Serpentine motility: Salmonella (Except S.gallonarum pullorum)

Detection of motility : Direct observation by hanging drop Direct observation by hanging drop Dark field microscopy Dark field microscopy Motility media Motility media

Flagellar staining Flagellar staining Electron microscopy Electron microscopy Immunological detection of “H” antigen Immunological detection of “H” antigen

Fimbriae Hair like surface appendages Hair like surface appendages nm thick nm thick Shorter thinner than flagella Shorter thinner than flagella Formed of protein subunits – Pilin Formed of protein subunits – Pilin

Functions Organs of adhesion Organs of adhesion Forms “Pellicles” Forms “Pellicles” Hemagglutination –Clumping of RBC’s (Escherichia,Klebsiella) Hemagglutination –Clumping of RBC’s (Escherichia,Klebsiella) Special type of Fimbriae called Sex pili,help in attachment to other bacteria Special type of Fimbriae called Sex pili,help in attachment to other bacteria

Endospores Highly resistant stages of bacteria Highly resistant stages of bacteria Spores germinate to form a single Vegitative cell. Spores germinate to form a single Vegitative cell. It is formed inside the cell. It is formed inside the cell. Eg: Bacillus, Clostridium

Endospore

Core contains the Nuclear body Core contains the Nuclear body Surrounded by a Spore Wall. Surrounded by a Spore Wall. Outside this is a thick Spore cortex Outside this is a thick Spore cortex This is covered in turn by a tough Spore coat. This is covered in turn by a tough Spore coat. Exosporium is additional outer covering, which exhibits ridges and grooves Exosporium is additional outer covering, which exhibits ridges and grooves

Factor responsible for the resistance of spores Presence of calcium dipicolinic acid Presence of calcium dipicolinic acid

Endospore inside bacteria

Position of Spores A = 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 forms Process of exhibiting variation in the shape and size of individual cells – Pleomorphism Process of exhibiting variation in the shape and size of individual cells – Pleomorphism Eg: H.influenzae Certain bacteria exhibit swollen and aberrant forms in ageing cultures – Involution forms Certain bacteria exhibit swollen and aberrant forms in ageing cultures – Involution forms This may be due to defective cell wall synthesis or due to Autolytic Enzymes This may be due to defective cell wall synthesis or due to Autolytic Enzymes Eg: Yersinia, Gonococcus

Protoplasts,Spheroplasts and L- Forms Removal of bacterial cell wall by hydrolysis with Lysozyme or antibiotics like Penicillin, liberates.. Removal of bacterial cell wall by hydrolysis with Lysozyme or antibiotics like Penicillin, liberates.. “Protoplasts” from Gram positive cells “Protoplasts” from Gram positive cells “Spheroplasts” from Gram negative cell “Spheroplasts” from Gram negative cell (retain the outer membrane and PG.)

When Protoplasts and Spheroplasts are able to grow and divide they are called the L-Forms. When Protoplasts and Spheroplasts are able to grow and divide they are called the L-Forms. First observed by Kleineberger-Nobel First observed by Kleineberger-Nobel Named it as L forms after Lister Institute London. Named it as L forms after Lister Institute London. Eg: Streptobacillus moniliformis

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