Free Bacteriology MCQs with Answers

• A. Spore formation
• B. Decreased virulence
• C. Prevent their phagocytosis
• D. Oxygen effect

Explanation: A bacterial capsule protects the organism from engulfment by phagocytes, helping it evade host immunity and remain virulent.

• A. Capsule
• B. Flagella
• C. Pili
• D. Mesosomes

Explanation: Pili, especially fimbriae, contain adhesins that bind specific receptors on host or other cell surfaces.

• A. Decease in virulence
• B. Loss of infectivity
• C. Inability to spread through tissue
• D. increase in invasiveness

Explanation: Loss of a capsule usually decreases virulence because the bacterium becomes more susceptible to phagocytosis and other host defences.

• A. Malaria
• B. Whooping cough
• C. Gas gangrene
• D. Wool sorters disease

Explanation: The Nagler reaction detects lecithinase activity of Clostridium perfringens, an important cause of gas gangrene.

• A. Acridine orange
• B. Thioglavin
• C. Congo red
• D. Auramine and Rhodamine

Explanation: Auramine-rhodamine fluorescent staining is used to screen sputum and other specimens for acid-fast Mycobacterium tuberculosis.

• A. Fungus
• B. Acid fast, non-motile bacillus
• C. Anaerobic, gram positive, non-acid fast bacteria.
• D. Retrovirus

Explanation: Actinomycosis is caused by Actinomyces, a branching, filamentous, anaerobic or microaerophilic Gram-positive bacterium that is…

• A. Unable to grow in the presence of oxygen
• B. Unable to grow in the absence of oxygen
• C. Able to grow in the presence of carbon dioxide
• D. Able to grow in the presence of absence of oxygen

Explanation: Facultative anaerobes can grow with or without oxygen, although many grow better when oxygen is available.

• A. Anthrax
• B. Typhoid
• C. Bacillary dysentery
• D. Cholera

Explanation: Anthrax is a zoonosis because Bacillus anthracis is maintained in animals and can pass to humans through infected animals or their…

• A. Alpha hymolytic streptococci (S. viridans)
• B. Staphylococci
• C. Beta hemolytic streptococci
• D. Pneumococci

Explanation: Viridans streptococci are alpha-haemolytic organisms that commonly colonise the mouth, throat and tonsils.

• A. Pleomorphism
• B. Elaboration of an enzyme that destroy penicillin
• C. Penicillin analogue production
• D. Lack of nucleic acid in the cell wall

Explanation: Many resistant Staphylococcus aureus strains produce beta-lactamase, an enzyme that hydrolyses the beta-lactam ring of penicillin.

• A. Facio-cervical actinomycosis
• B. Cutaneous anthrax
• C. Infected squamous cell carcinoma
• D. None of the above

Explanation: A malignant pustule is the characteristic skin lesion of cutaneous anthrax, caused by Bacillus anthracis.

• A. Salmonella
• B. Klebsiella
• C. Escherichia
• D. Paracolons

Explanation: Salmonella is a major intestinal pathogen that does not ferment lactose, so its colonies remain pale on MacConkey agar.

• A. E.coli
• B. Bacteroides
• C. Pseudomonas
• D. Klebsiella

Explanation: Bacteroides are obligate anaerobic Gram-negative bacilli and grow in the absence of oxygen. E.

• A. Streptococcus
• B. Staphylococcus
• C. E.coli
• D. Gonococci

Explanation: Staphylococci divide in several planes and remain attached, producing characteristic grape-like clusters.

• A. Lysozyme
• B. Fibrinolysin
• C. Coagulase
• D. S protein

Explanation: Coagulase converts fibrinogen to fibrin and forms a clot around pathogenic Staphylococcus aureus, helping it resist phagocytosis.

• A. Though plasmids
• B. Incorporating part of host DNA
• C. Through bacteriophages
• D. through conjugation

Explanation: Bacteria can acquire new characteristics through plasmids, bacteriophage-mediated transduction and conjugation.

• A. Syphilis
• B. Gonorrhea
• C. TB
• D. Tyhoid

Explanation: The Wassermann test is a historical complement-fixation test for syphilis caused by Treponema pallidum.

• A. Tularemia
• B. Diptheria
• C. Gonorrhoea
• D. All o f the above

Explanation: A lysogenic beta-phage carries the gene for diphtheria toxin, and its incorporation into Corynebacterium diphtheriae is called phage…

• A. It consists of a mixed polymer called peptidoglycon
• B. It is the structure principally responsible for the reaction of gram staining
• C. It is a unique flexible plastic structure
• D. It contains D-isomers of amino acids

Explanation: The bacterial cell wall is a rigid peptidoglycan structure, not a flexible plastic structure.

• A. Cl. difficile
• B. Staphylococcus
• C. Cl. welchii
• D. Cl. botulinum

Explanation: Staphylococcus aureus, Clostridium perfringens, and Clostridium botulinum are classic causes of food poisoning.