All Free Microbiology MCQs with Answers

• A. Lysozyme
• B. Secretozyme
• C. Albumin
• D. Isozyme

Explanation: Lysozyme is an antibacterial enzyme found in egg white and saliva that cleaves peptidoglycan in bacterial cell walls.

• A. Delayed reaction
• B. Immediate reaction
• C. passive transfer by serum
• D. None of the above

Explanation: Anaphylaxis is an immediate type I hypersensitivity reaction that can be passively transferred by serum containing IgE.

• A. IgG
• B. IgD
• C. IgM
• D. IgA

Explanation: IgA is the principal immunoglobulin in exocrine secretions such as saliva, tears, intestinal fluid and breast milk, where secretory IgA…

• A. Lysosomes
• B. Proteolytic enzymes
• C. Lymphotoxins
• D. Vasoactive mediators

Explanation: Mast-cell granules contain vasoactive mediators such as histamine, which cause vasodilation, increased vascular permeability and…

• A. Atopic allergy
• B. Serum sickness
• C. Transfusion reaction
• D. Contact dermatitis

Explanation: Serum sickness is a classic type III hypersensitivity reaction caused by deposition of circulating antigen-antibody immune complexes.

• A. C2a
• B. C3b
• C. C4a
• D. C5a

Explanation: C5a is the strongest chemotactic complement fragment and attracts neutrophils and other leukocytes to sites of inflammation.

• A. IgA
• B. IgD
• C. IgE
• D. IgG

Explanation: Secretory IgA is the predominant immunoglobulin in saliva and other mucosal secretions, where it prevents microbial attachment and…

• A. Salk vaccine
• B. Tetanus toxoid
• C. Sabin's oral vaccine
• D. All of the above

Explanation: The Salk polio vaccine contains inactivated poliovirus. Sabin vaccine uses live attenuated virus, while tetanus toxoid contains…

• A. Synovial fluid
• B. Myocardium
• C. Cardiac valves
• D. Vascular intima

Explanation: The group A streptococcal carbohydrate contains N-acetylglucosamine, which can cross-react with components of cardiac valves in rheumatic…

• A. CD 4*
• B. CD 8*
• C. B - lymphocytes
• D. None of the above

Explanation: Protection against tuberculosis is mainly cell-mediated and is initiated by CD4 helper T cells, especially Th1 cells, which activate…

• A. Hemoral immunity
• B. Cell mediated immunity
• C. Complement function
• D. Phagocyte dysfunction

Explanation: The tuberculin skin test is a delayed-type hypersensitivity reaction mediated by sensitised T lymphocytes, so it reflects cell-mediated…

• A. Boiling
• B. Ethanol
• C. Cidex
• D. All of the above

Explanation: HIV is readily inactivated outside the body by heat such as boiling, suitable concentrations of ethanol, and glutaraldehyde-based…

• A. Mycobacteria
• B. Spore
• C. Prions
• D. Coccidia

Explanation: Prions are the most resistant infectious agents to routine antiseptics, disinfectants and sterilisation methods because they contain…

• A. HIV
• B. Hepatitis C
• C. Hepatitis B
• D. Hepatitis E

Explanation: Dental instruments contaminated with blood can transmit HIV, hepatitis B, and hepatitis C.

• A. 1-2% cetrimide
• B. 100% alcohol
• C. 2% Lysol
• D. 5% chloroxylene

Explanation: Absolute alcohol is not a reliable disinfectant because water is needed for effective protein denaturation; about 70% alcohol is generally…

• A. Hot air oven
• B. Auto claving
• C. Irradiation
• D. Ethylene dioxide

Explanation: Oil and grease are moisture-free materials and are sterilized by dry heat in a hot-air oven.

• A. Glassware
• B. Rubber tubes
• C. Sharp instrument
• D. Liquid paraffin

Explanation: Hot-air ovens are suitable for glassware, metal sharp instruments and oils such as liquid paraffin.

• A. Ultra violet rays
• B. Ultrasonic vibrations
• C. Infrared rays
• D. Gamma rays

Explanation: Cold sterilisation uses ionising radiation, especially gamma rays, to destroy microorganisms without substantial heating.

• A. 125°C for new seconds
• B. 60°C for 15 minutes
• C. 72°C for 5 minutes
• D. 72° for 15 - 20 Sec

Explanation: Flash, or high-temperature short-time, pasteurisation heats milk to about 72°C for 15 seconds.

• A. Lysis
• B. Oxidation
• C. Hydrolysis of DNA
• D. Coagulation of proteins

Explanation: Dry heat kills microorganisms mainly by oxidative damage to cellular components, with dehydration also contributing.