Tests in Microbiology Lab - Microbiology for Lab Technicians

Microbiology for Lab Technicians - one year diploma

1. Tests in Microbiology Lab by, Miss Areesha Ahmad Senior Lecturer B.Sc (H), M.Sc , M.Phil and Ph.D scholar (Microbiology)

2. Tests in Microbiology Lab For lab technician students, microbiology tests are essential to develop practical skills in diagnosing infections, understanding microbial cultures, and conducting various diagnostic procedures. Here are some common Microbiology tests that should be covered:

3. 1. Gram Staining Purpose : To differentiate between Gram-positive and Gram-negative bacteria. Procedure : Staining with crystal violet, iodine, alcohol, and safranin . Result Interpretation : Purple (Gram-positive) or Pink/Red (Gram-negative).

4. 1. Gram Staining

5. 2. Acid-Fast Staining ( Ziehl-Neelsen Staining) Purpose : To identify acid-fast bacteria like Mycobacterium (e.g., tuberculosis ). Procedure : Use carbol fuchsin , acid-alcohol, and methylene blue . Result Interpretation : Acid-fast bacteria appear red; non-acid-fast appear blue.

6. 3. Culture Media Tests Types of Media : Nutrient Agar : General-purpose media for bacterial growth. MacConkey Agar : Selective for Gram-negative bacteria and differentiates lactose fermenters. Blood Agar : Used for detecting hemolysis (alpha, beta, gamma). Procedure : Inoculate specimens on media and incubate at optimal temperatures.

7. 3. Culture Media Tests

8. 4. Antibiotic Sensitivity Testing (Kirby-Bauer Disc Diffusion) Purpose : To determine bacterial susceptibility to antibiotics. Procedure : Discs containing antibiotics are placed on bacterial lawns on agar plates. Result Interpretation : Zones of inhibition around discs indicate sensitivity or resistance.

9. 5. Biochemical Tests Catalase Test : Purpose : To detect the presence of the catalase enzyme. Procedure : Adding hydrogen peroxide to bacteria. Bubbling indicates a positive result.

10. 5. Biochemical Tests Coagulase Test : Purpose : Differentiates Staphylococcus aureus (coagulase-positive) from other staphylococci. Procedure : Mixing bacteria with plasma to check for clot formation.

11. 5. Biochemical Tests Oxidase Test : Purpose : To identify bacteria producing cytochrome c oxidase (e.g., Pseudomonas ). Procedure : Oxidase reagent turns purple when positive.

12. 6. Urine Culture Purpose : Diagnose urinary tract infections (UTIs). Procedure : Inoculate urine on agar plates and check for colony growth. Result Interpretation : Significant growth indicates infection; colony count is important.

13. 7. Blood Culture Purpose : Detect bacteremia (presence of bacteria in blood). Procedure : Blood samples are inoculated into bottles containing media and incubated. Result Interpretation : Growth of organisms indicates a bloodstream infection.

14. 8. Stool Culture Purpose : Identify enteric pathogens (e.g., Salmonella , Shigella ). Procedure : Stool is plated on selective media like MacConkey and XLD agar. Result Interpretation : Pathogens show specific colony characteristics (color, shape).

15. 9. Microscopy of Wet Mount Preparations Purpose : Observe motility or structure of organisms, such as protozoa or fungi. Procedure : Place a drop of liquid specimen on a slide and observe under a microscope.

16. 10. ELISA (Enzyme-Linked Immunosorbent Assay) Purpose : Detect antigens or antibodies (e.g., in viral infections like hepatitis or HIV). Procedure : Sample is tested in microplate wells, and color change indicates a positive result.

17. 11. DNA Testing (PCR - Polymerase Chain Reaction) Purpose : Detect specific genetic material of microorganisms. Procedure : Amplifies DNA sequences to diagnose infections like tuberculosis or COVID-19.

18. 12. Hemolysis Test on Blood Agar Purpose : To identify types of hemolysis produced by bacteria, especially Streptococcus species. Result Interpretation : Alpha hemolysis: Greenish zone (partial hemolysis). Beta hemolysis: Clear zone (complete hemolysis). Gamma hemolysis: No hemolysis.