Detection of microorganisms (Diagnostic tests)

This is one of the developing areas of microbiology. There are two approaches in the laboratory diagnosis of infectious diseases.

1. bacteriologic methods
2. immunological (serological) methods

Selection of proper specimen, proper collection of the specimen, proper transportation and proper guidance of the laboratory personnel are the key issues in bacteriologic diagnosis of infectious diseases. All the steps should be carried out in correct way in order to obtain a good result.

If the infectious organism is difficult to isolate by bacteriological methods, we should move to the immunological methods. Immunological methods are expensive and this is the main drawback of this method.


Bacteriologic method

1. Blood cultures
2. Throat cultures
3. Sputum cultures
4. Spinal fluid cultures
5. Stool cultures
6. Urine cultures
7. Genital tract cultures
8. Wound and abscess cultures

Immunological methods

1. Identification of an organism with known serum

i. Capsular swelling (Quellung) reaction
ii. Slide agglutination test
iii. Latex agglutination test
iv. Counter immunoelectrophoresis test
v. Enzyme linked immunosorbent assay
vi. Fluorescent antibody tests

2. Identification of serum antibodies with known antigens

i. Slide or tube agglutination test
ii. Serological tests for syphilis
iii. Cold agglutinin test