Size of Microorganism Shape of Bacteria Morphology Physiology Classification Microorganism Difference between Gram Positive and Gram Negative Functions And Demonstration of Cell wall

1. MOPHOLOGY & PHYSIOLOGY OF BACTERIA
ANKUR VASHISHTHA
Assistant professor
IIMT University
Meerut

2. Classification of microorganism
Microorganism are grouped under both prokaryotes and eukaryotes.
Bacteria and blue green algae are placed under prokaryotes. They
have a primitive nucleus, and other properties of a prokaryotic cell.
Whereas other algae, fungi and parasites belong to eukaryotic
cellular organelles.
Virus are obligate intracellular parasite, that’s why they are not
grouped in prokaryotes and eukaryotes.

3. Size of microorganism
• Extremely small.
• Size of the bacteria is expressed in micrometers.
• Viruses are measured in nanometers.
• Most of the bacteria of medical importance generally measure 0.2 – 1.5µm in
diameter and about 3-5µm in length.
• Human pathogenic viruses range 20-300 nm in diameter.
• Because of the small size, microorganisms cannot be seen distinctly with the
unaided eye but need a microscope for their visualization.
• Most bacteria can be observed by light Microscope whereas virus need an electron
microscope.

4. Shape of bacteria
• Depending on their shape, bacteria are classified into:-
MICROORGANISM
Cocci Bacilli
Gram-Positive
Cocci
Gram-Negative
Cocci
Gram-Positive
Bacilli
Gram-Negative
Bacilli

5. • Cocci are oval, spherical shaped arranged in groups (Clusters), chain ,
tetrad, & pair.
• Bacilli are rod shaped & can be arranged in chain, pair and some bacilli are
curved, comma shaped, or cuneiform shaped.

7. Bacterial cell wall
• The cell wall is a thought and rigid structure . Surrounding the bacterium.
• It is 10-25nm in thickness and weighs about 20-25% of the dry weight of
the cell.

8. The cell wall has following functions
 Provides protection to the cell against osmotic lysis.
 Confers rigidity
 Accounts for the shape of the cell.
 Takes part in cell division.
 Protect a cell from toxic substances and is the site of action of several
antibiotics.
 Virulence factors-Bacterial cell wall contains certain virulence factors (e.g.
endotoxin), which contribute to their pathogen city
 Immunity: Antibody raised against specific cell wall antigens (e.g. antibody to
LPS) may provide immunity against some bacterial infection.

9. Gram Positive Cell wall
• Cell wall of gram positive is simpler than that of gram negative bacteria.
▫ Peptidoglycan layer:- is much thicker (50-100 layer thick, 16-18nm).
▫ Each layer is a mucopeptide chain, composed of alternate units of N-
acetyl muramic acid and N-acetyl glucosamine molecules.
▫ Teichoic acid:- the teichoic acid constitute major surface antigens of
GPB. They are water solubule polymers.

10. Gram negative Cell wall
• Gram-negative cell wall is thinner and more complex than the gram-positive cell wall,
▫ Peptidoglycan layer:- it is very thin (1-2 layer, 2nm thick).similar to that of GPB
cell wall.
▫ Outer membrane:- this is a phospholipid layer
 It serves as a protective barrier of the cell.
 Outer membrane proteins or porin proteins.(Specialized protein).
Lipopolysaccharide:- It consists of three parts
1. Lipid A or the endotoxin
2. Core polysaccharide
3. O antigen
 Periplasmic space:- it is the space between the inner cell membrane and outer
membrane.

11. Gram +ve bacterial cell wall Gram -ve bacterial cell wall

12. Differences between Gram positive and
Gram negative cell wall
Characters Gram Positive cell
wall
Gram Negative cell
wall
Peptidoglycan layer Thicker (15-80nm) Thinner (2nm)
At 3rd position of tetrapeptide side chain L- Lysine present Mesodiaminopimelic
acid present
Pentaglycine bridge Present Absent
Lipid content Nil or scanty (2-5%) Present(15-20%)
Lipopolysaccharide Absent Present(endotoxin)
Teichoic acid Present Absent
Variety of amino acids Few Several
Aromatic amino acids Absent Present

13. Demonstration of cell wall
• Cell wall cannot be seen by light microscope and does not
stain with simple dyes. Demonstration of cell wall can be done
by methods such as:-
▫ Plasmolysis
▫ Microdissection
▫ Differential stain
▫ Reaction with specific antibody
▫ Electron microscope

14. THANK
YOU