All Free Microbiology MCQs with Answers

• A. Vegetative forms
• B. Spore forms
• C. Both of the above
• D. None of the above

Explanation: Disinfection destroys or removes many vegetative microorganisms from surfaces but does not reliably destroy bacterial spores.

• A. 140°C x 2 hrs. x 10 lbs pr.
• B. 121°F x 15 mts. x 15 lbs pr.
• C. 121°F x 15 sec. x 15 lbs pr.
• D. 121°C 15 mts. x 15 lbs pr.

Explanation: The standard autoclave cycle is 121°C at about 15 psi for 15 minutes, allowing saturated steam to destroy microorganisms and spores.

• A. Kill mircobes
• B. Remove microbes
• C. Inhibit microbial growth
• D. Dehydrate microbial cells

Explanation: Soap mainly lifts microbes, oils, and organic material from the skin so they can be removed by rinsing; it does not necessarily kill them.

• A. Disinfectant
• B. Moist heat sterilisation
• C. Antibiotics
• D. Dry heat sterilization

Explanation: The Rideal-Walker test measures a disinfectant's efficiency by comparing its activity with phenol, producing a phenol coefficient.

• A. Pathogens killed but spores are not affected
• B. Only pathogenic micro-organisms killed
• C. Non-pathogenic killed
• D. All pathogenic and non-pathogenic microorganisms killed

Explanation: Sterilisation means complete destruction or removal of all forms of microbial life, including pathogenic and non-pathogenic organisms and…

• A. Boiling at 100°C
• B. Disinfection by hypochlorite solution
• C. Autoclave
• D. Pasteurisation

Explanation: A properly operated autoclave destroys bacterial spores through saturated steam under pressure, typically at 121°C.

• A. 3 minutes
• B. 15 minutes
• C. 30 minutes
• D. 60 minutes

Explanation: At 134°C, a pre-vacuum autoclave can sterilize properly prepared surgical instruments in about 3 minutes.

• A. Pasteurization
• B. Autoclave
• C. Kochs sterilizer
• D. hot air oven

Explanation: An autoclave uses saturated steam under pressure, raising the temperature above the normal boiling point and denaturing microbial…

• A. Gram positive organisms
• B. Gram negative organisms
• C. Mycoplasma
• D. Virus infections

Explanation: ICU-acquired pneumonias are classically dominated by Gram-negative bacilli, including Pseudomonas, Klebsiella and Acinetobacter, although…

• A. Cryptococcosis
• B. Tuberculosis
• C. Candidiasis
• D. Aspergilosis

Explanation: Candidiasis, especially oral thrush, is among the commonest opportunistic infections in AIDS because impaired cell-mediated immunity…

• A. exotoxin production
• B. lecithinase production
• C. hypersensitivity
• D. Coagulase production

Explanation: Many fungi cause disease through tissue invasion or hypersensitivity reactions, and hypersensitivity is the best choice among the listed…

• A. Penicillium
• B. Aspergillus
• C. Mucor
• D. Rhizopus

Explanation: Aspergillus commonly forms an aspergilloma, or fungal ball, within a pre-existing cavity such as an old tuberculosis cavity.

• A. Tellurite medium
• B. NNN medium
• C. Chocolate agar medium
• D. Sabourauds medium

Explanation: Sabouraud’s dextrose agar is the standard culture medium for many fungi because its acidic pH and formulation favour fungal growth while…

• A. Brain - heart infusion
• B. Sabouraud's
• C. Sabouraud's plus antibiotics
• D. Any medium incubated at 35-37°C

Explanation: Sabouraud’s medium supplemented with antibiotics selectively supports fungi while suppressing bacterial contaminants.

• A. Subcutaneous tissue
• B. Systemic organs
• C. Nails, hair and skin
• D. Superficial skin and deep tissue

Explanation: Dermatophytes digest keratin and infect keratinised tissues, namely the skin, hair and nails.

• A. Methylene blue dextrose agar
• B. Saboraud's medium
• C. Pingolevin
• D. All of the aboveParasites & Parasitic Diseases

Explanation: Sabouraud's dextrose agar is the routine culture medium for Candida and many other fungi because its acidic environment favours fungal…

• A. Yeast like fungus
• B. Forms Chlamydospores
• C. Blastomeres seen in isolates
• D. Seen in immunocompromised and causes meningitis in them

Explanation: Candida albicans is a yeast-like fungus that forms chlamydospores and can cause invasive disease, including meningitis, in…

• A. Penicillium
• B. Mucor
• C. Aspergillus
• D. All of the above

Explanation: Penicillium, Mucor and Aspergillus can all cause opportunistic infections, particularly in patients with impaired immunity.

• A. Kerison
• B. Alopecia areata
• C. Pilomatrixoma
• D. Tenia incognito

Explanation: Kerion is the painful, boggy, indurated inflammatory form of tinea capitis, often complicated by secondary bacterial infection.

• A. Candida albicans
• B. Mucor
• C. Cryptococcus
• D. Aspergillus

Explanation: The Reynolds-Braude phenomenon is germ-tube formation by Candida albicans when incubated in serum, an important presumptive identification…