Bacterial Morphology.ppt by Dr. Rakesh Prasad Sah

1. Bacterial Morphology
By Dr. Rakesh Prasad Sah
Associate Professor,
Microbiology

2. Introduction
• Microorganisms are living structures of microscopic in size.
• Bacteria  belongs to group Prokaryotes.
S.No. Structure Prokaryotes Eukaryotes
Nucleus
1. Nuclear membrane Absent Present
2 Nucleolus Absent Present
3 Chromosome One > One
4 Deoxyribonucleoprotein Absent Present
5 Division Binary fission Mitosis
Cytoplasma
6 Mitochondria, Golgi apparatus, Lysosomes,
Endoplasmic reticulum
Absent Present
Chemical Composition
7 Sterols Absent Present
8 Muramic acid Present Absent

3. SIZE OF BACTERIA
• Unit for measurement :
Micron or micrometer,μm:
1μm=10-3mm
• Size:
Varies with kinds of bacteria,
and also related to their age and
external environment.
• Cocci: sphere, 1μm
• Bacilli: rods , 0.5-1 μm in width -3 μm in length
• Spiral bacteria: 1~3 μm in length and 0.3-0.6 μm in width

4. Bacterial Morphology

5. Bacterial Cell
• Prokaryotes
– No true nucleus
– No organelles
• Divide-binary fission

6. Parts of Cell
• Cell Envelope
– Cell wall
– Cell membrane-plasma
membrane, cytoplasmic
membrane
– Capsule
• Cytoplasm
– Nucleoid
– Ribosomes
– Granules/Inclusion bodies
– Mesosomes
• Spores
• Plasmids
• Appendages
– Pilli
– Flagella

7. • Is a tough & rigid structure surrounding the bacterium like a shell.
• Weighs about 20-25% of the dry weight of the cell.
• Functions
– Accounts for shape of cell
– Provides protection to the cell against osmotic damage.
– Confers rigidity upon bacteria
– Takes part in cell division.
– Possesses target site for antibiotics, lysozymes and bacteriophages.
– Carries bacterial antigens that are important in virulence and immunity.
Cell Wall

8. • Rigid part of cell wall  peptidoglycan  mucopeptide (murein)
composed of N-acetyl muramic acid and N-acetyl glucosamine
alternating in chains, cross linked by peptide subunits.

10. Cell Wall
S.N
o.
Character Gram Positive Gram Negative
1 Peptidoglycan Thicker (50-100 layers,
16-80nm)
Thinner (1-2 layers,
2nm)
2 Teichoic acid Present Absent
3 Lipids Absent or Scanty (2-5%) Present (15-20%)
4 Periplasmic space Absent Present

11. Gram Positive Cell Wall
• Peptidoglycan:- thicker (16-80nm) than gram negative
bacteria (2nm).
• Teichoic acid
– Contains in a significant amount which is absent in gram negative.
– Constitute major surface Ags
– Two types (wall teichoic acid and lipoteichoic acid)

12. Special components of Gram
positive cell wall
Teichoic acid

13. Gram Negative Cell Wall
• Gram negative cell wall  complex structure with following
components
– Lipoprotein layer
– Outer membrane
– LPS (Lipopolysaccharide):-
• constitutes endotoxin of GNB
• Determine major surface Ag
• Toxicity (pyrogenicity, lethal effect, tissue necrosis)
– Periplasmic space
– Peptidoglycan

14. Gram Negative Cell Wall
• Lipoprotein Layer
– Connects the peptidoglycan to outer membrane
• Outer membrane
– Contains certain proteins called as OMP (outer membrane protein).
– Target sites for antibiotics and bacteriocins.
• Lipopolysaccharides (LPS)
– Consist of lipid A attached to a polysaccharide
– Constitutes the endotoxin of GNB.
• Periplasmic space
– Space between inner and outer membrane
– Contains various binding proteins for specific substrates.
• Peptidoglycan

15. Special Components of
Gram negative cell wall

16. • Rigid part of cell wall  peptidoglycan  mucopeptide (murein)
composed of N-acetyl muramic acid and N-acetyl glucosamine
alternating inchains, cross linked by peptide subunits.

17. Demonstration of Cell Wall
• Plasmolysis
– Bacteria  placed in hypertonic saline, shrinkage of cytoplasm occurs 
while cell wall retains original shape and size.
• Microdissection
• Differential staining
• Reaction with specific Ab
• Electron microscopy

18. • Bacteria without cell walls or with deficient cell walls are of
four types:-
• Mycoplasma
– Naturally occurring bacteria without cell wall.
• L-forms
– Kleineberger-Nobel  studying Streptobacillus moniliformis in Listure
institute London  observed abnormal forms of the bacteria and named
them L-forms after Lister institute.
– Develop either spontaneously or in the +ce of penicillin  due to
interference with synthesis of cell wall.
• Protoplast
• Spheroplast
Bacteria with Defective Cell Wall

19. Bacteria with Defective Cell Wall
• Synthesis of cell wall  interfered or inhibited by many factors :-
– Antibiotics
– Bacteriophage
– Lysozyme
Enzyme +nt in many
tissue fluids
Lyses succeptible
bacteria by splitting
linkage of peptidoglycan
in the cell wall.
Lysozyme
Lysozyme
Lysozyme
Gram Positive
Bacteria
Gram Negative
Bacteria
In Hypertonic Solution
Protoplast
Spheroplast

20. Cytoplamsic Membrane
• Is 5-10nm thick elastic
semipermeable layer  lies
beneath cell wall separating it
from cell cytoplasm.
– Acts as an osmotic barrier.
– Acts as a semipermeable
membrane controlling the inflow
and outflow of metabolites to and
from the protoplasm.
– Contains enzymes necessary for
cell wall synthesis (cytochrome
oxidase, enzymes of tricaboxylic
acid).

21. Cytoplasm
• Is a colloidal system containing variety of organic and inorganic
solutes in a viscous watery solution.
• Lacks
– Mitochondria
– Endoplasmic reticulum
• Contains
– 70% water of bacterial mass
– Ribosomes (site for Protein synthesis)
– Mesosomes (Bacterial respiration, cell wall formation and chromosome
replication)
– Vacuoles
– Inclusions bodies (tiny particles found freely suspended and floating within the
cytoplasmic matrix)
– Nucleoid

22. Ribosomes
• Centre for protein synthesis.
• Are composed of
– Ribosomal RNA (rRNA) and
– Ribosomal proteins.
Intracytoplasmic inclusions
• Source of stored energy
• Are grown under conditions of nutritional deficiency and disappear
when deficient nutrients are supplied.
• Volutin or metachromatic granules are +nt in C. diptheria.
Metachromatic granules of
C. diptheria by Albert Stain

23. Nucleoid
• Bacteria don't have true nucleus and there is no nuclear membrane
or nucleolus.
• Nucleiod is present  irregularly shaped region containing DNA.
• Bacterial DNA  is haploid  replicates by simple binary fission
and maintains bacterial genetic characteristics.
• Some bacteria may possess extra-nuclear genetic material in the
cytoplasm consisting of DNA named as Plasmids or episomes.

24. Capsule and Slime layer
• Is amorphous viscid bacterial secretion  surrounds outermost
layer of bacteria  when diffuses into surrounding medium and
remains as a loose undermarcated secretion as Leuconostoc (made up
of Cellulose contains Glucoses & fructose) known as “Slime layer” 
when it is organized into a defined structure  known as “Capsule”.
E.g. Streptococcus pneumoniae.
• Capsule  which are very thin and can not be demonstrated under light
microscope are called “Microcapsule”. E.g. Neisseria meningitidis.
• Is polysaccharide in nature.

26. Functions
• Antiphagocytic in nature.
• Antigenic
• Virulence
Demonstration of capsules
• India ink staining (negative staining)
• Serological method
– Quellung phenomenon

27. Capsule (Polysaccharides)  colonies are mucoid

28. Flagella
• Cytoplasmic appendages
protruding through cell wall.
• Composed of a protein (flagellin)
(5-20µm in length and 0.01-
0.02µm in diameter.)
• Organ of locomotion.
• All motile bacteria  contains
either one or more flagella.
(except spirochetes).

29. Parts and composition
• Three parts
– Filament
– Hook
– Basal body

30. Arrangements/Types
• Monotrichous
• Lophotrichous
• Amphitrichous
• Peritrichous

31. Demonstration
• Dark ground illumination
• Electron microscopy
• Indirect methods
– Spreading type of growth on a medium e.g. swarming growth of
Proteus sp.
– Motility under microscope e.g. hanging drop preparation
– Spreading of bacteria in semisolid agar e.g. Craigie’s tube method.

32. Fimbriae
• Hair like appendage projecting from cell surface as straight
filaments.
• Also called as “Pili”.
• Composed of protein called Pilin.
• Unrelated to motility.
• Types
– Common pili
– Sex or F pili
– Col I pili

33. • Functions
– Adhesion
– Transfer of genetic material (sex pili is +nt in male bacteria. Help the
male cells to attach with female cells in forming conjugation tubes 
through which genetic materials is believed to be transferred from male
to female; thus helps in bacterial conjugation)
• Detection
– Electron Microscopy
– Haemagglutination
• Clinical Significance
– Sex pilli has role in conjugation  helps in transfer of genetic material;
Transfer of R factor by conjugation is very important method of drug
resistance in bacteria.

34. Endospores
• Are highly resistant resting stage formed in unfavorable
environmental conditions
– Depletion of nutrients.
• Sporulation is not a method of reproduction as bacteria is not divide
during sporulation.
• In the process of sporulation
each vegetative cells  one spore and
during subsequent germination
each spore  one vegetative bacterium.

35. Morphology of Spore
• Core
• Spore membrane
• Spore cortex
• Spore coat
• Exosporium

36. Shape and Position of Spores
• Position:
– Central
– Sub-terminal or
– Terminal.
• Shape: Oval or spherical.
• Width:
– Non-bulging spore, or
– Bulging spore.

37. Resistance
• Are extremely resistant to
– Ordinary boiling
– Disinfectant
– Heating
• Resistance of spore is due to high content of “Calcium and
Dipicolinic acid”
• Are destroyed by autoclaving at 1210C for 15mins.
• Demonstration
– Modified ZN-staining (0.25-0.5% Sulphuric acid instead of 20%)

38. • Uses
– Biological indicator to check the sterilization process e.g. Autoclave, Hot
air oven, Ethylene oxide sterilizer.
• Spore forming bacteria
– B. anthracis, B. subtilis, Cl. tetani, Cl. welchii, Cl. botulinum

40. MCQs
1. Periplasmic space is absent in……………….
2. Teichoic acid is present in ………………………
3. Gram positive cell wall have ………………peptidoglycan layer.
4. Bacteria divide by………………
5. Lysozyme acting on Gram positive bacteria in hypertonic
solution leads to formation of………………..
6. Lysozyme acting on Gram negative bacteria in hypertonic
solution leads to formation of………………..

41. 7. Intracytoplasmic inclusion bodies will formed
under………………………conditions and they are source of
………… of energy.
8. The main function of Capsule is to………………………………
9. Demonstration of capsule can be done by………………..and
…………….reaction.
10.Bacterial colonies are mucoid due to presence of……………
11.Organ of locomotion in bacteria is……………….

42. 1. All motile bacteria posses one or more flagella
except………………..
2. Flagella is made up of a protein called……………..
3. The arrangement of Flagella all around the body of bacteria is
called……………..
4. A tuft of flagella at one end is called…………..
5. A tuft of flagella at both end is called……….
6. Endospores are highly resistant due to presence of
…………&…………….