Diagnosis Of Bacterial Diseases

APPLIED MICROBIOLOGY Lab Diagnosis of Bacterial Diseases I.

Involves following steps: • • • • • • 9 9 9

II.

Collection of specimen Demonstration of Bacteria and their products Isolation : Culture Biochemical and Agglutination tests for identification Animal inoculation tests Serology for antibody titre Specimen should be properly collected, well chosen and of good quality. High risk specimen must be indicated on the label e.g. Hepatitis B or HIV infected. Transport to the lab should be made without delay and if delay is inevitable then specimen should be collected in transport media

Detection of bacteria and their products is done by: Microscopy:

• Direct demonstration : Provides rapid diagnosis • Immunofluorescence : Many organisms can be detected by immunofluorescent antibody staining e.g. Legionella pneumophila, Chlamydia trachomatis etc. • Period Acid Schiff (PAS) and Methenamine silver staining : can detect parasites in tissues.

III. Culture: Specimen inoculated in suitable medium an incubated aerobically an unaerobically is put on a battery of biochemical and agglutination tests to identify the organism.

IV. Detection of Antibodies: 5-10 ml of blood is allowed to clot; serum is separated by centrifugation after half an hour and is put for serological tests and antibiotic assays. Other body fluids like pleural, pericardial, cerebrospinal, urine and saliva etc. can also be used occasionally. “Paired sera” are the samples collected at weekly intervals are tested for detection of rise of antibody titre. Antibodies against whole organism or only against one class of antigen can be detected.

V.

Quality Control: It refers to meeting predetermined requirements and includes appropriateness. It ensures a reasonable degree of consistency in the findings and results for better patient service.

Two Types

Internal quality control • Equipments should be properly serviced • Media and reagents should be regularly checked • Laboratory personnel should be competent • Lab techniques should be up-todate

External quality check • Simulated specimens prepared centrally are sent to participating laboratories for reporting on the specimen within a given time. Thus performance of participating labs is assessed regularly.