Microbiology Multiple Choice Questions on “Microbial Virulence Factors”.
1. Which bacteria has an unusual capsule among the following?
A. Haemophilus influenzae
B. Klebsiella pneumoniae
C. Streptococcus pneumoniae
D. Bacillus anthracis
Answer: D
Clarification: The capsule of B. anthracis is unusual in that it is composed of a polypeptide rather than a polysaccharide.
2. For Clostridium botulinum type A toxin, 1 MLD for a mouse is ____________
A. 2.5 X 10-5 µg
B. 4 X 10-5 µg
C. 6 X 10-2 µg
D. 5 µg
Answer: A
Clarification: Clostridium botulinum type A produces the most potent toxin known: 1 MLD for a mouse is 2.5 X 10-5 µg of the purified toxin.
3. What is the chemical nature of endotoxins?
A. protein
B. polysaccharide
C. lipopolysaccharide
D. lipid
Answer: C
Clarification: Endotoxins are lipopolysaccharide in nature and are released from cell walls of lysed Gram-negative bacteria.
4. Exotoxins are heat-labile in nature.
A. True
B. False
Answer: A
Clarification: Exotoxins are heat-labile in nature and are inactivated easily by boiling which is not the case with endotoxins.
5. Which type of toxin is tetanus toxin?
A. enterotoxin
B. neurotoxin
C. cytotoxin
D. endotoxin
Answer: B
Clarification: Tetanus toxins affect nerve tissues and are hence termed as neurotoxins. It comes under the broad category of exotoxins.
6. Which of the following is a plasmid-mediated toxin?
A. diphtheria toxin
B. botulism toxin
C. tetanus toxin
D. food-poisoning toxin
Answer: D
Clarification: Plasmid-mediated toxin is the enterotoxin made by food-poisoning strains of S.aureus. Plasmid carries the gene for the toxin.
7. The B region of diphtheria toxin has the enzymatic activity.
A. True
B. False
Answer: B
Clarification: By means of the B region the toxin binds to the membrane of a tissue cell. The A region consists of the enzymatic activity and catalyzes the reaction that inactivates elongation factor 2 (EF-2), a factor essential for elongation of polypeptide chain during protein synthesis.
8. Which amino acid is an inhibitory transmitter?
A. alanine
B. tyrosine
C. glycine
D. phenylalanine
Answer: C
Clarification: To render neurons temporarily insensitive to stimulation, it is accomplished in the central nervous system by the action of a chemical called an inhibitory transmitter, viz., the amino acid glycine.
9. Which toxin causes paralysis of muscles?
A. Diphtheria toxin
B. Botulinum toxin
C. Tetanus toxin
D. Cholera toxin
Answer: B
Clarification: The botulinum toxin binds to the axon near the neuromuscular junction and prevents the secretion of acetylcholine; thus the muscle cannot contract and paralysis occurs.
10. How many B subunits are present in cholera toxin?
A. 1
B. 2
C. 3
D. 5
Answer: D
Clarification: Cholera toxin consists of one A subunit and five B subunits. The B subunits are responsible for attachment of the toxin to the surface of the epithelial cells of the small intestine.
11. Which of the following statement is wrong regarding the effects of cholera toxin?
A. loss of fluid from the body
B. pH of blood remains constant
C. hemoconcentration
D. bicarbonate ions are lost from blood
Answer: B
Clarification: Since bicarbonate ions are lost from the blood, the pH of the blood falls, which may lead to death by acidosis.
12. Which of the following toxin is a hemolysin?
A. diphtheria toxin
B. botulism toxin
C. tetanus toxin
D. streptolysin O
Answer: D
Clarification: Streptolysin O (SLO) is a hemolysin, causing beta hemolysis around the colonies on blood-agar plates incubated anaerobically. It also acts as a leukocidin.
13. Hylauronidase enzyme is produced by which of the following organism?
A. C. perfringens
B. S. pyogenes
C. S. aureus
D. Mycoplasma
Answer: A
Clarification: Hylauronidase enzyme is produced by the gas gangrene causing organism C. perfringens and has been thought to enhance penetration of the host tissues by hydrolyzing hyaluronic acid.
14. Which of the following has the ability to bind antibodies?
A. Coagulase
B. Streptokinase
C. Protein A
D. Hydrogen Peroxide
Answer: C
Clarification: Protein A is located on the cell wall of S. aureus and has the ability to bind antibodies, regardless of their specificity. The antibody molecules are distorted and their binding site is exposed.
15. LT toxin is produced by _____________
A. S. aureus
B. E.coli
C. B. anthracis
D. C. perfringens
Answer: B
Clarification: LT toxin is produced by E.coli and it is an enterotoxin, causing diarrhea. The mechanism is similar to that of cholera toxin.
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