All Free Microbiology MCQs with Answers

• A. Produced by gram negative bacteria
• B. Produced by gram positive bacteria
• C. Not secreted outside the cell
• D. Cannot be toxoided

Explanation: Endotoxin is the lipopolysaccharide component of the outer membrane of Gram-negative bacteria, and it is usually released when cells break…

• A. M protein
• B. Pyrogenic exotoxin
• C. Streptolysin 0
• D. Carbohydrate cell wall

Explanation: Toxic shock syndrome is caused by a superantigenic pyrogenic exotoxin, especially TSST-1 produced by Staphylococcus aureus.

• A. cell wall
• B. cell membrane
• C. Nuclear material
• D. Mesosomes

Explanation: The major structural difference is in the cell wall: Gram-positive bacteria have a thick peptidoglycan layer, whereas Gram-negative…

• A. VDRL
• B. Kahn's test
• C. TPHA
• D. Widal test

Explanation: TPHA detects antibodies specifically directed against Treponema pallidum and is therefore a treponemal test.

• A. Budding
• B. Binary fission
• C. Sporing
• D. Bacterial components produced by host cells

Explanation: Most bacteria reproduce asexually by binary fission, in which the chromosome replicates and one cell divides into two genetically similar…

• A. Escherichia coli
• B. Klebsiella pnemoniae
• C. Proteus miribilis
• D. Pseudomonas aeruginosa

Explanation: Pseudomonas aeruginosa is an oxidase-positive Gram-negative rod that produces the characteristic blue-green pigment pyocyanin and commonly…

• A. Borrelia burgolorferi
• B. Chalamydia trachomatis
• C. Leptospira interrogans
• D. Treponema pallidum

Explanation: Syphilis is caused by Treponema pallidum, a motile spirochaete transmitted mainly through sexual contact.

• A. Eosin stain
• B. Haemotoxin stain
• C. Ninhydrin stain
• D. Blue stain

Explanation: Ninhydrin reacts with amino groups and produces a coloured compound, making the marked or wetted region on filter paper easier to see.

• A. -20°C to -7°C
• B. -7°C to + 20°C
• C. 25°C to 40°C
• D. 55°C to 80°C

Explanation: Mesophiles grow best at moderate temperatures, commonly about 25°C to 40°C, with many human pathogens having an optimum near 37°C.

• A. 10%
• B. 2%
• C. 5%
• D. 15%

Explanation: Agar is usually used at about 1.5% to 2% to solidify culture media while still permitting diffusion of nutrients and growth of colonies.

• A. Introduction of complex media
• B. Discovery of Rabies Vaccine
• C. Discovery of M. Tuberculosis
• D. Disproved spontaneous regression theory

Explanation: Louis Pasteur developed the rabies vaccine, introduced complex culture media, and disproved spontaneous generation.

• A. Internal structures are differentiated in living cells
• B. Internal structures are differentiated in dead cells
• C. Internal metabolic activities can be observed
• D. External capsule formation can be observed

Explanation: Phase-contrast microscopy converts small differences in refractive index into contrast, allowing internal structures of living, unstained…

• A. Wd miller
• B. Leumenhoek
• C. Robertson
• D. Socranci

Explanation: Antonie van Leeuwenhoek first described oral microorganisms as tiny ‘animalcules’ after observing dental plaque microscopically.

• A. Different refractive indices of object
• B. Different reflective indices of object
• C. Light scattering
• D. Light attenuation

Explanation: Phase-contrast microscopy converts differences in refractive index and thickness into visible differences in brightness and contrast.

• A. dna
• B. Ribosome
• C. Mitochondria
• D. Cell wall

Explanation: Bacteria are prokaryotes, so they lack membrane-bound organelles such as mitochondria.

• A. Lag phase
• B. Log phase
• C. Stationary phase
• D. Decline phase

Explanation: Sporulation usually begins in the stationary phase when nutrients are depleted and environmental stress increases.

• A. in the presence of oxygen
• B. in the presence of nitrogen
• C. in the absence of oxygen
• D. differential media

Explanation: Anaerobic bacteria grow without oxygen because oxygen is toxic to them or cannot be used for their metabolism.

• A. Treponema pallidum
• B. Mycobacterium leprae
• C. N. gonorrhoeae
• D. None of the above

Explanation: None of these organisms fulfils every classical Koch postulate: Treponema pallidum and Mycobacterium leprae cannot be routinely grown in…

• A. Unicellular
• B. Free living
• C. Having either DNA or RNA
• D. Cell wall containing muramic acid

Explanation: Bacteria are cellular organisms containing both DNA and RNA, whereas viruses contain either DNA or RNA as their genetic material.

• A. Psychrophiles
• B. Mesophiles
• C. Cryophiles
• D. Thermophiles

Explanation: Most pathogenic bacteria are mesophiles because they grow best at moderate temperatures, typically around 20–45°C, with human pathogens…