Free Bacteriology MCQs with Answers

• A. E coli
• B. Bifido bacteria
• C. Staphylococcus
• D. Salmonella

Explanation: Bifidobacteria are normal intestinal organisms widely used as probiotics because they can support the gut microbial balance.

• A. M. Kansasii
• B. M. ulcerans
• C. M. chelonae
• D. M. smegmatis

Explanation: Mycobacterium chelonae is a rapidly growing nontuberculous mycobacterium associated with injection-site abscesses and outbreaks from…

• A. Caused by Calymmatobacterium granulomatis
• B. Lymphadenopathy is remarkable & diagnostic
• C. Penicillin is drug of choice
• D. Characterized by painful genital ulcers

Explanation: Donovanosis is a sexually transmitted ulcerative infection caused by Calymmatobacterium granulomatis, now called Klebsiella granulomatis.

• A. Syphilis
• B. Tuberculosis
• C. Gonorrhea
• D. Lymphoma

Explanation: The Kolmer test is a complement-fixation screening test historically used for syphilis by detecting antibodies against Treponema pallidum.

• A. Direct microscopy
• B. Culture
• C. ELISA
• D. DNA probe

Explanation: The organism must first be cultured and then tested with antimicrobial susceptibility methods such as disc diffusion or broth dilution.

• A. Rickettsiae
• B. Mycoplasma
• C. Chlamydiae
• D. Ehrlichiae

Explanation: Mycoplasma lacks a true peptidoglycan cell wall, making it naturally resistant to antibiotics that act on cell-wall synthesis, such as…

• A. Trichrome Methylene blue
• B. Carbol Fuschin
• C. Acid Fast Stain
• D. Calcoflour White

Explanation: An abattoir worker with a papule progressing to an ulcer suggests cutaneous anthrax, caused by Bacillus anthracis.

• A. Fungi
• B. Gram +ve bacteria
• C. Virus
• D. Gram -ve bacteria

Explanation: Endotoxin is lipopolysaccharide, specifically lipid A, in the outer membrane of Gram-negative bacteria and is released mainly during cell…

• A. Pseudomonas
• B. coli
• C. Proteus
• D. Staphylococcus

Explanation: Weil-Felix testing uses Proteus strains, especially OX19, OX2 and OXK, because their antigens cross-react with rickettsial antibodies.

• A. Transduction
• B. Transformation
• C. Mutation
• D. conjugation

Explanation: Conjugation commonly spreads antibiotic-resistance plasmids, or R factors, directly between bacteria and is an important source of…

• A. Staphylococcus
• B. Streptococcus
• C. Gonococcus
• D. Mycobacterium

Explanation: Dorset's egg medium is an egg-based medium used for cultivating Mycobacterium, particularly tubercle bacilli.

• A. Loefflers serum slope
• B. Mc Conkey
• C. Saboraud agar
• D. Lowenstein Jensen medium

Explanation: Loeffler's serum slope supports rapid growth and enhances metachromatic granules in Corynebacterium diphtheriae, helping its recognition.

• A. L-J medium
• B. Robertson cooked meat medium
• C. Loefflers medium
• D. Sabourauds agar

Explanation: Robertson cooked meat medium supports the growth of anaerobes because the cooked meat reduces the oxidation-reduction potential and…

• A. Protein polysaccharide complex
• B. Heat labile
• C. Highly potent
• D. Has specific tissue affinity

Explanation: Exotoxins are usually soluble proteins, heat labile, highly potent, and specific in their tissue effects.

• A. Clostridia
• B. S. epidermidis
• C. Choleria
• D. Mycobacterium

Explanation: Robertson's cooked meat medium is reducing and therefore provides suitable anaerobic conditions, especially for Clostridium species.

• A. The bacteria should be able to be isolated from a diseased tissue
• B. When inoculated in experimental animals bacteria may or may not cause disease
• C. Pure cultures can be obtained
• D. Bacteria should be able to be isolated from the diseased tissue in the experimental animals

Explanation: Koch's postulates require the isolated organism to reproduce the disease in a healthy experimental host, not merely may or may not cause…

• A. Louis pasteur
• B. Robert koch
• C. Hensen
• D. Ogston

Explanation: Robert Koch introduced practical solid culture media, allowing bacteria to grow as separate colonies for isolation and identification.

• A. Lipid-polysaccharide complex
• B. Protein compound
• C. Lipoprotein
• D. None

Explanation: Exotoxins are soluble protein toxins actively secreted by certain bacteria, unlike endotoxin, which is the lipopolysaccharide component of…

• A. Lag
• B. Exponential growth
• C. Stationary phase
• D. Decline

Explanation: The stationary phase has approximately zero net growth because new cell formation balances cell death as nutrients become limited and…

• A. Actinomyces israelii
• B. Candida albicans
• C. Mycobacterium tuberculosis
• D. Streptococcus mutan

Explanation: Mycobacterium tuberculosis has a lipid-rich, mycolic-acid cell wall and is poorly stained by the Gram method, so it is identified by…