All Free Microbiology MCQs with Answers

• A. Growing bacteria in adverse environment
• B. Growing bacteria in unconventional host
• C. Serial passage in an experimental host
• D. Repeated cultures in artificial media

Explanation: Attenuation is commonly produced by adverse conditions, growth in an unusual host, or repeated culture on artificial media.

• A. Bile solubility
• B. Optochin sensitivity
• C. Bacitracin sensitivity
• D. Cataslase positive

Explanation: Chains of Gram-positive cocci with haemolysis suggest a Streptococcus, and bacitracin sensitivity supports identification of Streptococcus…

• A. Escherichia Coli
• B. Staphylococci
• C. Spirochetes
• D. Mycoplasma

Explanation: Mycoplasma lacks a peptidoglycan cell wall and is consequently naturally resistant to antibiotics that inhibit cell-wall synthesis, such…

• A. Cell wall of Gram positive organisms
• B. Cell wall of Gram negative organisms
• C. Cytoplasm of Gram positive organisms
• D. Cytoplasm of Gram negative organisms

Explanation: Teichoic acids are characteristic components of Gram-positive cell walls, where they contribute to wall structure and antigenic…

• A. Sabourauds medium
• B. Agar - agar
• C. Lowenstein Jensen medium
• D. Loefflers serum slope

Explanation: Lowenstein-Jensen medium is an egg-based selective medium used to isolate Mycobacterium, especially M. tuberculosis.

• A. Involved in multidrug resistance transfer
• B. Involved in conjugation
• C. Imparts capsule formation
• D. Imparts pili formation
• E. Both A & B

Explanation: Plasmids may carry antibiotic-resistance genes and can also contain genes enabling conjugative transfer between bacteria.

• A. Staphylococcus
• B. Micrococcus
• C. Sarcina
• D. Aerococcus

Explanation: Sarcina cells divide in three perpendicular planes and remain attached, producing the characteristic cubical packets of eight or more…

• A. Salmonella
• B. Klebsiella
• C. Spirochetes
• D. Bacillus

Explanation: Smith-Noguchi medium is an enriched medium historically used for growing delicate spirochetes.

• A. Bordetella
• B. Brucella
• C. Borrelia
• D. None of the above

Explanation: Noguchi medium is associated with the cultivation of Borrelia, a group of pathogenic spirochetes.

• A. Gram's staining
• B. Fontana's staining
• C. India ink preparation
• D. Zheil-Neilson's staining

Explanation: India ink is a negative stain because the dark dye stains the background while leaving the bacterial cell clear, often revealing a capsule…

• A. Monotrichate
• B. Peritrichate
• C. Bipolar
• D. Lophotrichate

Explanation: A tuft of several flagella arising from one pole is called lophotrichous arrangement.

• A. are proteins
• B. are heat labile
• C. are highly antigenic
• D. activate complement by the alternate pathway

Explanation: Endotoxin is lipopolysaccharide, especially lipid A, and is heat stable, weakly antigenic and not a protein.

• A. wall
• B. nucleus
• C. membrane
• D. Capsule

Explanation: Detergents disrupt the bacterial cytoplasmic membrane by damaging its lipid structure, causing leakage of essential cell contents.

• A. Treponema
• B. Actinomyces
• C. Streptococcus
• D. Mycobacterium

Explanation: Treponema pallidum is a thin, motile spirochaete that is difficult to see with ordinary bright-field microscopy, so dark-field microscopy…

• A. Blood agar
• B. Selenite F Broth
• C. Mac Conkey agar
• D. Nutrient Broth

Explanation: Selenite F broth is an enrichment medium that selectively enhances the growth of Salmonella from specimens containing mixed intestinal…

• A. Resistance transfer factor (RTF)
• B. Colicigenic factor (Col)
• C. Fertility factor (F+)
• D. All of the above

Explanation: The resistance transfer factor is a plasmid carrying genes for resistance to several antibiotics and can transfer them between bacteria.

• A. Incubator
• B. anaerobic jar
• C. Refrigerator
• D. Centrifuge

Explanation: An anaerobic jar removes oxygen or replaces it with an oxygen-free atmosphere, allowing anaerobes to grow.

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

Explanation: Spirochaetes are very thin, flexible bacteria that are difficult to see with ordinary bright-field microscopy but can be visualised by…

• A. Aquatic bodies are main habitat
• B. It can replicate in amoeba
• C. Urine test is a reliable method
• D. Person to person transmission

Explanation: Legionella pneumophila is acquired mainly from contaminated water aerosols and can multiply within amoebae; urinary antigen testing is…

• A. Aerobic bacterial disease
• B. Anaerobic bacterial disease
• C. Aerobic fungal disease
• D. Anaerobic fungal disease

Explanation: Actinomycosis is caused by Actinomyces, a filamentous Gram-positive anaerobic or microaerophilic bacterium, not a fungus.