Laboratory methods for identification of Bacteria
Once bacterial colony obtained in for culture. Bacteria can be identified by studying characteristics;
1. Morphology
2. Staining
3. Cultural characteristics
4. Resistance
5. Metabolism
6. Biochemical reactions
7. Antigenic structure
8. Bacteriophage and bacteriocin typing (ability to test strain)
9. Pathogenicity
10. Rapid identification method
11. Morality test
12. Serological diagnosis
13. Antibiotic sensitivity test
1. Morphology (Physical characteristics)
Morphology of bacterium depends on a number of factor such as;
Strain studies
Nature of culture medium
Age of culture and number of cell culture
Temperature and time of incubation
Characteristics of bacterium are;
Shape
Size
Arrangement
Motility
Capsules
Spore
Flagella
All these characteristics studies by staining, hanging drop preparation, dark ground illumination, phase contrast and electron microscopy.
2. Culture characteristics
Consistent growth and of microorganisms depend on adequate supply of nutrient and favourable environmental condition in which growth is supported.
Provide information for identification of bacteria.
Studying colonies on solid media features such as;
Shape, size, edge, consistency, colony colour.
It helps to identify individual type of bacteria.
In liquid medium; degree of growth (maximum and minimum temperature are noted), presence of turbidity, nature of surface growth , pellicle formation, quality and order.
For example; Broth culture media
3. Resistance
Resistance of organism to heat and to disinfectant is tested both for vegetative and spore forms.
Resistance to antibiotic and chemotherapeutic agents and bacteriocins would help in differentiation and identification of bacterial characters.
4. Metabolism
Requirements of oxygen, CO2 and other nutrients, capacity to form pigment helps in classification and identification of aerobic and anaerobic bacteria.
5. Biochemical reaction
Citrate utilization
Sugar fermentation
Urease test
Lactose fermenting test
Coagulase test; tube test, slide test
Growth in KCN
Indole production
6. Immunological method
Involve interaction of bacterial antigen with antibody (produce by host immune system).
For example; ELISA, TRF, IMS-ECL
7. Antigenic structure or serological test
We can identify bacteria by agglutination or other serological reaction.
Immuno- flourescent test is useful in some cases.
8. Pathogenicity
For pathogenicity test commonly used laboratory animal. Today a large number of in vitro test are available.
9. Rapid identification method
Identification is simplified by detection of specific enzymes, toxins, antigen or metabolic end product of isolated bacteria.
10. Staining
Staining is technique used to enhance contrast in samples, generally at microscopic level.
It help to study;
Morphology
Size
Arrangement of bacteria
Detection of other cellular material
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