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I have all the questions from the image. I can answer these microbiology MCQs from my knowledge with high confidence - these are standard MBBS 2nd year microbiology questions. Let me provide the complete answer key with explanations.
Microbiology MCQ Answer Key
Department of Microbiology - MBBS 2nd Professional Pre-University Exam 2024
Q1. Graft transplant between two genetically non-identical members of the same species?
Answer: c) Allograft ✓ (marked on paper)
- Autograft - same individual
- Isograft - genetically identical (twins)
- Allograft - same species, genetically different (most common transplants)
- Xenograft - different species
Q2. Used to demonstrate bacterial capsules?
Answer: b) India ink ✓ (marked on paper)
India ink (negative staining) creates a dark background, making the clear capsule visible as a halo around the organism. Albert's stain is for diphtheria granules; Ziehl-Neelsen is for acid-fast bacilli.
Q3. Endoscopes are sterilized by?
Answer: b) Glutaraldehyde ✓ (marked on paper)
Endoscopes are heat-sensitive and cannot tolerate autoclaving or hot-air oven. 2% glutaraldehyde (Cidex) is the standard method for high-level disinfection/sterilization of endoscopes.
Q4. Agar-agar is used in microbiological media as?
Answer: c) Solidifying agent ✓ (marked on paper)
Agar is a polysaccharide extracted from red algae. It is used purely as a solidifying agent - it has no nutritive value for bacteria. It melts at 100°C and solidifies at 42°C, making it ideal. Nutrients must be added separately.
Q5. Griffith typing of streptococci is based on?
Answer: b) Hemolysis on blood agar ✓ (marked on paper)
Griffith's classification (1934) divides streptococci based on the type of hemolysis on blood agar:
- Alpha (α) - partial/green hemolysis
- Beta (β) - complete/clear hemolysis
- Gamma (γ) - no hemolysis
(Note: Lancefield grouping is based on carbohydrate C antigen; M protein is a virulence factor of Group A strep.)
Q6. Concentration of glutaraldehyde for high-level disinfection?
Answer: a) 2% ✓ (marked on paper)
2% activated (alkaline) glutaraldehyde is the standard concentration for high-level disinfection. At this concentration it achieves sporicidal activity in 3-10 hours.
Q7. Microbiological waste colour bag?
Answer: a) Yellow ✓ (marked on paper)
As per Biomedical Waste Management Rules:
- Yellow - infectious/microbiological/anatomical waste (incinerated)
- Red - contaminated/recyclable plastic waste
- Blue - glass/metallic waste
- Black - general waste
Q8. Which shows "falling leaf" motility?
Answer: a) Entamoeba histolytica ✓ (marked on paper)
Entamoeba histolytica shows characteristic "falling leaf" or "tumbling leaf" motility, moving by pseudopodia in a unidirectional manner. This is a key identifying feature on wet mount microscopy.
Q9. Earliest immunoglobulin to appear on the surface of B cells?
Answer: b) IgM ✓ (marked on paper)
IgM is the first immunoglobulin expressed on the surface of developing B lymphocytes (as monomeric surface IgM). It is also the first antibody produced during a primary immune response. IgD appears alongside IgM on mature naive B cells.
Q10. Best method for disposal of human anatomical waste?
Answer: b) Incineration ✓ (marked on paper)
Human anatomical waste (body parts, organs, tissues) must be disposed of by incineration as per biomedical waste management guidelines. This completely destroys the waste and eliminates infection risk.
Q11. Culture medium with low redox potential required for growth of?
Answer: a) Clostridium tetani ✓ (marked on paper)
Clostridium tetani is a strict anaerobe - it requires a very low oxygen tension/redox potential for growth. Media like Robertson's cooked meat medium (RCMM) provide these anaerobic conditions. Pseudomonas and E. coli are aerobes/facultative anaerobes.
Q12. Most important specimen for Salmonella Typhi isolation in the first week of enteric fever?
Answer: a) Blood ✓ (marked on paper)
During enteric fever:
- Week 1: Blood culture (bacteremia phase) - highest yield (~85-90% positive)
- Week 2: Blood + Bone marrow + Stool
- Week 3 onwards: Stool and urine
- Bone marrow is actually the gold standard, but blood is the most important/commonly used specimen in week 1.
Q13. Patch test is done for which type of reaction?
Answer: d) Contact dermatitis ✓ (marked on paper)
Patch test detects Type IV hypersensitivity (delayed-type hypersensitivity), which underlies contact dermatitis (e.g., allergy to nickel, rubber, cosmetics). The allergen is applied under occlusion for 48 hours and read at 48-72 hours.
- Atopy = Type I (IgE-mediated) - tested by skin prick test
- Arthus reaction = Type III (immune complex)
- Schwartzman = non-immunological phenomenon
(Note: The paper appears to have "b) Atopy" marked, but the correct answer is d) Contact dermatitis.)
Q14. NIH swab is used to collect samples for?
Answer: Pinworm/Enterobius vermicularis infection (Roundworm infection - a)
The NIH (National Institutes of Health) swab, also called the "Scotch tape" or cellophane tape method equivalent, is used to collect perianal samples for Enterobius vermicularis (pinworm) eggs, which are deposited around the perianal region at night.
Summary Answer Key
| Q | Answer | Key Concept |
|---|---|---|
| 1 | c) Allograft | Same species, genetically different |
| 2 | b) India ink | Negative staining for capsules |
| 3 | b) Glutaraldehyde | Heat-sensitive instruments |
| 4 | c) Solidifying agent | Agar = no nutritive value |
| 5 | b) Hemolysis on blood agar | Griffith's classification |
| 6 | a) 2% | High-level disinfection |
| 7 | a) Yellow | Biomedical waste rules |
| 8 | a) Entamoeba histolytica | Falling leaf motility |
| 9 | b) IgM | First surface Ig on B cells |
| 10 | b) Incineration | Anatomical waste disposal |
| 11 | a) Clostridium tetani | Strict anaerobe |
| 12 | a) Blood | Week 1 typhoid fever |
| 13 | d) Contact dermatitis | Type IV hypersensitivity |
| 14 | a) Roundworm/Enterobius | NIH swab - perianal |
All marked answers on the paper are correct except Q13 where "Atopy" is marked but the correct answer is Contact dermatitis. Patch test specifically tests for Type IV hypersensitivity (contact dermatitis), not Type I (atopy).
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