ELEMENTARY MICROBIOLOGY 

Microbiology & prasitology

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Microbiology:

Microbes( microorganisms) include unicellular organism which are not visible to eye. Following table indicates the living agent responsible for disease in decreasing order size.

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Living agent of disease

Macroscopic:

Helminthes( Worms)

( seen by Naked Eye)

Microscopic):

protozoa, Bacteria,Micoplasma, Rickettsia

Spirochaetes Ultramicroscopic:

viruses(seen only in electronic microscope)

Out of these:

Helminthes,arthopods and protozoa belong to animal kingdom,while bacteria, mycoplasma, Rickettsia, spirochaetes belong to plant kingdom.

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Bacteria:

Minute, unicellular, organism. They have no cholrophil. They multiply by binary fission. They possess enzymes and have their own metabolism.

Morphology:

(a) size- smaller ones( cocci) measure 0.8 to 2u in diameter and larger ones( bacil) 1.2 to 12u in length. Bacteria occur in 3 basic shapes.

(1) spherical - cocci

(2) Reshaped- bacillli

(3) spiral- vibrios, spirochaetes.

Cocci may be oval or flattened on the side, bacil may be have round or pointed ends,vibrois are comma shaped, spirochaetes are elongated flexible organsim twisted spially along the long asixs.

Motillity:

Many organsim are motile when suspend in a suitable fluid medium. Motillity is due to hairlike projection called flagellge. Motillity is studied by hanging drop preparation ( cholera organsim). Dark ground illumination ( syphilis organsim).

For better visualization staining methods are used.

1) Gram’s stain organsim are divided as gram+ ve( violet) Gram negative ( pink)

2) Ziehl Neeteen stain- acid fast bacteria ( Tuberculosis)

Other stains are used to demonstrate capsule of bacteria or granules present in bacteria etc.

Growth requirement of bacteria:

For rapid multiplication of bacteria they require

1. Food- an organic source of carbon and nitrogen.

2. Moisture

3. Temperature

4. Reaction- usually all bacteria grow at pH 7.2 of human body.

5. Oxygen- If oxygen is required they are called aerbes, if they grow in absence of oxygen they are called annaerobes.

6. CO2 :- gonorrhoea requires cO2 

In the laboratory bacteria grow on culture media:

1) simple media- all organsim can grow normally e.g Nutrient agar.

2) Enriched media- specific Nutrent is added for that organisim like blood agar.

3) selective media- only organsim required to be grown will multiply, other will be inhibited by specific substance.

( Lowenstein Jenson medium in Tuberculosis).

Biochemical Reactions:

1) Bacteria can ferment organic substance and produce acid and gas. This can be ultillized in laboratory for identification of organisim.

2) proteolytic

3) production of H2 S

4) Gelatin is liquified

Certain bacteria under unfavorable conditions of growth get covered by resisting membrane and these forms which are resistant to enviroment are called spores. These spores are resistant to drying,boliling and remain without food and water for years. This common bacteria producing spores are tetanus,arthrax, botulinum,calustridum welchii. For sterilization of instrument from spores autoclaving, gultaraldehyde, elthylene oxide are required.

 

Antigen and antibody recation:

Immune mechanism is stimulate by bacteria,viruses, Rickettsiae. Antigens (microbes) stimulate reticuloendothelial system.

Common Anitibody recation:

1) Agglutination:

The antigen is soulable but collection of antigen and antibody gives visible precipitation or turbidity.

These recation are normally specific hence used disease.

A) ledentification of living agent of disease.

B) Diagnosis of disease.

C) In Epidemogical studies.

D) In detecting immune status of individual.

 

1) Agglutination recation:

Commonly used in thypoid ( widal test) ( Typhus fever) ( weil Flexi recation) and Bacteria.

2) precipitation reaction:

a) Khan and VIDAL tests in syphilis.

b) Agar gel diffusion test was used in small pox and now used for hepatitis B

3) complement fixation test:

e:g Wasserman man test in syphilis

Pathogenicity:

Capacity of causative agent to produce disease is know as pathogenicity. Virulence : the This means ability of agent to produce servere illness.