Bacterial anatomy
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Bacterial Anatomy. Rashmi.S. Anatomy of a Bacterial Cell. Description. Bacteria are Prokaryotic, unicellular that do not contain chlorophyll. Size of bacteria may range from 0.2-1.5 micrometer in diameter and 3-5 micrometer in length. DIFFERENCES BETWEEN PROKARYOTES AND EUKARYOTES.

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  • Bacteria are Prokaryotic, unicellular that do not contain chlorophyll.

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

Differences between prokaryotes and eukaryotes

Character Prokaryotes Eukaryotes


Nuclear Membrane Absent Present

Nucleolus Absent Present

Mitotic Division Absent Present


Cytoplasmic Streaming Absent Present

Pinocytosis Absent Present

Lysosomes Absent Present

Golgi Apparatus Absent Present

Endoplasmic Reticulum Absent Present

Chemical Composition

Sterols Absent Present

Muramic Acid Present Absent

Teichoic Acid Present Absent

Classification of bacteria based on their shape
Classification of Bacteria based on their Shape

  • Cocci

  • Bacilli

  • Vibrio

  • Spirilla

  • Spirochetes

  • Actinomycetes

  • Mycoplasma

Cellular arrangement
Cellular Arrangement

In Cocci,

  • Diplococci: Cocci arranged in pairs

  • Streptococci: Arranged in chains

  • Staphylococci: Arranged in grape like clusters

In Bacilli,

  • Coccobacilli: Oval shaped

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

  • Streptobacilli: In chains





Structure of a bacterial cell bacterial anatomy
Structure of a Bacterial Cell(Bacterial Anatomy)

  • Examination of a bacterial cell reveals components of structures

  • Some external to cell wall

  • Others internal to cell wall

Demonstration of the cell wall
Demonstration of the cell wall

  • Plasmolysis

  • Microdissection

  • Specific Antibodies

  • Differential Staining

  • Electron Microscope

Structure of the cell wall
Structure of the cell wall

  • Bacterial cell wall provides structural integrity to the cell.

  • The bacterial cell wall differs from that of all other organisms by the presence of Peptidoglycan

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

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

  • Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape

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

Gram positive cell wall
Gram Positive Cell wall

  • The Gram positive cell wall is characterized by the presence of a very thick Peptidoglycan layer

  • 20-80 nm thick

  • Cell wall contains90% Peptidoglycan and 10%Teichoic acid

Gram negative cell wall
Gram Negative Cell Wall

  • Gram negative cell wall contains a thin Peptidoglycan layer adjacent to the 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.

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

  • Polysaccharide determining O antigen

  • Core Polysaccharide

  • Glycolipid portion /Lipid A

Cytoplasmic membrane
Cytoplasmic Membrane activities………

  • It is a thin layer lining the inner surface of the cell wall.

  • Semipermiable membrane controlling the flow of metabolites

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

Cytoplasm activities………

  • Colloidal system of variety of organic and inorganic solutes in Viscous watery solution

  • No ER,& Mitochondria

  • Contains Mesosomes Inclusions and Vacuoles

Mesosomes activities………

  • Vesicular, convoluted invaginations of the plasma membrane

  • Prominent in GM+ bacteria

  • Principal sites of Respiratory enzymes

  • Analogous to mitochondria in Eukaryotes

Nucleus activities………

  • Bacterial nuclei “have no nuclear membrane “or the nucleolus.

  • 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.

Plasmids activities………

  • Extra chromosomal DNA

  • Circular capable of autonomous replication.

  • Transferred from one bacterium to another .

Importance activities………

  • Their presence confers certain special characters……

  • Toxigenicity

  • Antibiotic Resistance

  • Ability to use certain unusual components as nutrients

Structures external to bacteria
Structures external to Bacteria activities………

  • Capsule

  • Flagella

  • Pili(Fimbriae)

Capsule activities………

  • Viscid material secreted by bacteria around the cell surface

  • Capsule is a sharply defined, organized structure (Eg: Pneumococcus)

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

Capsular Staining activities………

Quellung reaction
Quellung Reaction activities………

  • Described by Neufeld(1902).

  • 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.

  • Used to type Pneumococci.

Functions of capsules
Functions of Capsules activities………

  • Antiphagocytic,thus contribute “Virulence”.

  • Protects against “Lysozyme”

  • Promote attachment of bacteria to surface(Eg: Streptococcusmutans).

  • Permits bacteria to adhere to Medical Implants & Catheters.

  • Toxicity to host cell – Eg: activities………Bacteroidesfragilis.

  • Provide protection against temporary drying.

  • Block the attachment ofBacteriophages.

Applications: activities………

  • Used in serological typing

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

  • Used in preparation of vaccines

    Eg: H.influenzae

Flagella activities………

  • Unbranched, long ,filaments ,made up of protein “Flagellin”

  • Organs of locomotion

  • Found in all motile bacteria except Spirochetes

Structure activities………

  • 3-20 Micrometer.

  • Each flagellum consists of 3 parts



    3.Basal body

Flagellar Arrangement activities………

Kinds of Motility activities………:

  • Darting motility : V.cholerae

  • Tumbling motility: L.monocyctogenes

  • Cork &screw motility: T.pallidum

  • Stately motile : Clostridium spp.

  • Serpentine motility: Salmonella (Except S.gallonarum pullorum)

Detection of motility : activities………

  • Direct observation by hanging drop

  • Dark field microscopy

  • Motility media

  • Flagellar staining activities………

  • Electron microscopy

  • Immunological detection of “H” antigen

Fimbriae activities………

  • Hair like surface appendages

  • 0.5-10 nm thick

  • Shorter thinner than flagella

  • Formed of protein subunits – Pilin

Functions activities………

  • Organs of adhesion

  • Forms “Pellicles”

  • Hemagglutination –Clumping of RBC’s (Escherichia,Klebsiella)

  • Special type of Fimbriae called Sex pili,help in attachment to other bacteria

Endospores activities………

  • Highly resistant stages of bacteria

  • Spores germinate to form a single Vegitative cell.

  • It is formed inside the cell .

    Eg: Bacillus, Clostridium

Endospore activities………

  • Core contains the Nuclear body activities………

  • Surrounded by a Spore Wall.

  • Outside this is a thick Spore cortex

  • This is covered in turn by a tough Spore coat.

  • Exosporium is additional outer covering, which exhibits ridges and grooves

Factor responsible for the resistance of spores activities………

  • Presence of calcium dipicolinic acid

Endospore inside bacteria activities………

Position of Spores activities………

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
Pleomorphism and Involution forms activities………

  • 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

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

    Eg: Yersinia, Gonococcus

Protoplasts spheroplasts and l forms
Protoplasts,Spheroplasts and L-Forms activities………

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

  • “Protoplasts” from Gram positive cells

  • “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.

First observed by Kleineberger-Nobel

Named it as L forms after Lister Institute London.

Eg: Streptobacillus moniliformis

THANK YOU divide they are called the