BACTERIAL MORPHOLOGY

BACTERIAL MORPHOLOGY

typical cell
Typical Bacterial Cell

PROTOSTA:

Divided in to

1. EUKARYOTES &

2. PROKARYOTES

Difference:

  Prokaryotes Eukaryotes
NUCLEUS
Nuclear Membrane Absent Present
Nucleolus Absent Present
Chromosome One Multiple
Nucleo-protein Absent Present
Division Binary Fission Mitosis
CYTOPLASM
Mitochondria Absent Present
Golgi apparatus Absent Present
Lysosomes Absent Present
E Reticulum Absent Present
CHEMICALS
Sterols Absent Present
Muramic acid Present Absent

SHAPE & ARRANGEMENT:

Shape & Arrangement of Bacterial Cells
Shape & Arrangement of Bacterial Cells
  • Cocci: Oval/Spherical shape
    • In pair: Diplococci
    • Chain: Streptococci
    • Group of four: Tetrads
    • Eight: sarcina
    • Cluster: Staphylococci
  • Bacilli: Rod shape
    • Coccobacilli: length slightly more then width (e.g.: Brucella)
    • Streptobacilli: bacilli in chain
    • Chinese letter pattern: Corynebacterium
    • Comma shaped: curved (e.g.: Vibrio)
  • Spirochaetes: Slender, flexous spiral (e.g.: Treponema)
  • Actinomycetes: Branching filamentous bacteria having rigid cell wall
  • Mycoplasmas: Cell wall deficient(no stable shape), very small in size(50-300nm)
  • Rickettsiae and Chlamydiae: small, obligate parasite, grows only on living cell.

 

CELL WALL:

Structure of Gram Negative Bacterial Cell Wall
Structure of Gram Negative Bacterial Cell Wall

Shell (10-25 nm)

Functions:

⇒ Shape

⇒ Rigidity

⇒ Protection (osmotic changes)

⇒ Cell division

⇒ Antigens (virulence & immunity)

Structure:

N-acetyl muramic acid (NAM), N-acetyl glucosamine(NAG)
N-acetyl muramic acid (NAM), N-acetyl glucosamine (NAG)
  • Gram Negative Bacteria:

1. Lipopolysaccharides: Endotoxin

⇒ Lipid A – Toxicity

⇒ Polysaccharides – Surface (O) antigen

2. Outer Membrane: Target site (antibiotic, phages)

⇒ Outer Membrane Protein

3. Periplasmic space:

⇒ Lipoproteins (anchor OM – PG)

4. Peptidoglycan: Mucopeptide (2 mm)

⇒ N-acetyl muramic acid (NAM)

⇒ N-acetyl glucosamine (NAG)

⇒ Peptide Subunits (cross link)

  • Gram Positive Bacteria:

    Structure of Gram Positive Bacterial Cell Wall
    Structure of Gram Positive Bacterial Cell Wall

1. Teichoic acid: Surface antigens

⇒ Ribotol or glycerols

2. Peptidoglycan: Mucopeptide 16-80 nm

3. Protein & Polysaccharides

Demonstration:

⇒ Plasmolysis: hypertonic saline

⇒ Micro dissection

⇒ Differential Staining

⇒ Antibody reaction

⇒ Electron Microscopy

  • Defective / Abnormal Cell Wall:

1. Mycoplasma:

⇒ Naturally occurring cell wall less bacteria

2. L-forms: Kleineberger; Lister Institute-London

⇒ Streptobacillus moniliformis

⇒ Interference with cell wall synthesis

⇒ Penicillin

3. Protoplast:

⇒ Gram positive bacteria

⇒ Lysozyme & hypertonic medium

4. Spheroplast:

⇒ Gram negative bacteria

⇒ Penicillin

⇒ Remnant of cell wall retained

5. Pleomorphism & Involution forms

⇒ Defective cell wall synthesis

⇒ Variation in size and shape of cell

⇒ Swollen and Aberrant forms

CYTOPLASMIC MEMBRANE:

  • 5-10 nm, elastic & semi permeable layer
  • Structure: Lipid bilayer
  • Functions:
    • Osmotic barrier
    • Enzymes (synthesis & destruction)
    • Control Inflow & outflow of metabolites

CYTOPLASM:

  • Colloidal system – organic and inorganic solutes
  1. Ribosome:
    Ribosome
    Ribosome
    • rRNA, 10-20 nm size, 70S (Svedberg unit)
  1. Inclusions:
  • Sources of stored energy
  • Nutritional deficiency states
    • Polymetaphosphate- volutin
    • Lipid polysaccharides- starch or glycogen
    • Sulphur granules
  1. Mesosomes:
  • Vesicular invagination of plasma membrane
  • Centers of respiratory enzymes
  • Septal and lateral mesosomes
  • Septal – chromosome associated (binary fission)

NUCLEUS:

  • No nuclear membrane
  • Basic proteins absent
  • Circular dsDNA- 1000 µm
  • Haploid; Multiplication – Binary fission
  • Plasmid – Drug resistance and toxigenicity

CAPSULE:

  • Amorphous viscid secretion
  • Slime layer or Capsule
  • Polysaccharide
  • Growth characters – Mucoid colonies
  • Functions:
    • Virulence- inhibit phagocytosis
    • Protection- phages, phagocytes, enzymes
    • Capsular antigen
  • Demonstration:
    1. Staining
      • India ink
      • Capsular staining
    2. Serological method
      • Quellung phenomenon / Neufeld reaction

FLAGELLA:

Flagellum
Flagellum
  • Cytoplasmic appendages
  • Protein (flaggelin) structure
  • 5-20 µm long x 0.01 µm thick
  • Organ of locomotion
  • Structure:
    • Filament
    • Hook
    • Basal body- outer and inner rings
  • Types:
    • Monotrichous; single polar flagellum
    • Amphitrichous; single bipolar flagella
    • Lophtrichous; multiple, single/bipolar flagella
    • Peritrichous; flagella all around cell
  • Demonstration:
    1. Dark ground illumination
    2. Flagellar staining
    3. Electron microscopy
    4. Motility demonstration
    5. Spreading growth on solid medium
    6. Hanging drop preparation
    7. Spreading growth in semisolid agar

FIMBRIAE:

Structure of Flagellum
Structure of Flagellum
  • Hair like appendages
    • to 1.0 µm long x 10 nm thick
  • Pilin protein, antigenic
  • Gram negative bacteria (100-500)
  • Fresh isolates and liquid cultures.
  • Types:
    • Common pili
    • Sex / Fertility pili (20µm)
    • Colicin pili
  • Functions:
    1. Adhesion
    2. Conjugation
  • Demonstration:
    1. Electron microscopy
    2. Hemagglutination

SPORE:

Germination of Spore
Germination of Spore
  • Highly resistant forms
  • Unfavourable environmental conditions
  • Morphology:
    • Exosporium
    • Spore coat
    • Spore cortex
    • Spore membrane
    • Core
  • Shape & Position:
    • Central (Bulging/Non-bulging)
    • Subterminal (Bulging/Non-bulging)
    • Terminal (Bulging/Non-bulging)
  • Resistance:
    • Autoclaving: 1210C / 15LBS / 15 Minutes
  • Demonstration:
    1. Gram staining
    2. Modified Ziehl-Neelsen
  • Use:
    • Control of sterilization (autoclave)
    • e.g. Bacillus stearothermophilus