Morphology & Physiology of Bacteria

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.

6. 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.

7. 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.

8. 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.

9. 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 Lipid A or the endotoxin Core polysaccharide O antigen Periplasmic space :- it is the space between the inner cell membrane and outer membrane.

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

11. 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 3 rd 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

12. 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

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