Category: MICROBIOLOGY Objective Questions

Microbiology Multiple Choice Questions on “Characteristics and Definition of Chemical Agents”.

1. A chemical agent that kills the microorganisms and is commonly applied to substances used on inanimate objects are _______________
A. Antiseptics
B. Sanitizer
C. Disinfectants
D. Antibiotics
Answer: C
Clarification: Disinfectant is a chemical agent that kills the growing forms but not necessarily the resistant spore forms of disease-producing microorganisms. They are commonly applied to substances used on inanimate objects.

2. An agent that prevents the growth of bacteria are known as __________________
A. Bactericide
B. Bacteriostatic
C. Antimicrobial
D. Antibiotic
Answer: B
Clarification: An agent that prevents or inhibits the growth of bacteria are known as bacteriostatic agents and the condition is known as bacteriostasis.

3. For using any chemical agent, we need to increase the temperature of the environment.
A. True
B. False
Answer: B
Clarification: One of the characteristics of chemical agents is that they should be toxic to microorganisms at room or body temperature. In using the compound, it should not be necessary to raise the temperature beyond that normally found in the environment where it is to be used.

4. Which of the following is the characteristics of a sanitizer?
A. destroys all microbial forms
B. prevents the growth or action of microorganisms
C. reduces the microbial population to safe levels
D. kills all the bacteria and the bacterial spores
Answer: C
Clarification: Sanitizer is an agent that reduces the microbial population to safe levels as prescribed by public health requirements. Usually it is a chemical agent that kills 99.9% of the growing bacteria and are generally applied to inanimate objects.

5. Which of the following is not a chemical agent for microbial control?
A. Radiations
B. Antibiotics
C. Antiseptics
D. Germicide
Answer: A
Clarification: Radiations are physical agents for microbial control and include ionizing as well as non-ionizing radiations to kill the microorganisms.

6. Escherichia coli is much more resistant to cationic disinfectants than Staphylococcus aureus.
A. True
B. False
Answer: A
Clarification: Chemical agents are not all equally effective against bacteria, fungi, and other microorganisms. Differences exist between Gram-positive and Gram-negative bacteria:
Escherichia coli is much more resistant to cationic disinfectants than Staphylococcus aureus.

7. The process of killing all microorganisms along with their spores is ____________________
A. Disinfection
B. Antisepsis
C. Sanitization
D. Sterilization
Answer: D
Clarification: Sterilization is the process of destroying all forms of microbial life. The term sterilization refers to the complete absence or destruction of all microorganisms and should not be used in a relative sense.

8. Which of the following are generally applied on living animal tissues?
A. Antiseptics
B. Disinfectants
C. Preservatives
D. Sanitizer
Answer: A
Clarification: Antiseptics are substances that opposes sepsis,i.e., prevents the growth or action of microorganisms either by destroying microorganisms or by inhibiting their growth and metabolism. They are usually applied on living animal tissues.

.

Microbiology Multiple Choice Questions on “Preservation of Foods”.

1. The temperatures used for canning foods ranges from ____________________
A. 0-20 degree C
B. 20-60 degree C
C. 60-100 degree C
D. 100-121 degree C
Answer: D
Clarification: The temperatures used for canning foods ranging from 100 degrees C for high-acid foods to 121 degrees C for low-acid foods.

2. In the high-temperature short-time (HTST) method of pasteurization, milk is exposed to a temperature of _________
A. 132 degree F
B. 145 degree F
C. 161 degree F
D. 120 degree F
Answer: C
Clarification: The HTST process employs equipment capable of exposing milk to a temperature of 161 degrees F (71.7 degrees C. for 15 secs.

3. Sterilization occurs at high temperatures for long periods of time.
A. True
B. False
Answer: B
Clarification: Sterilization exposes milk to ultrahigh temperatures for very short periods of time, for example, 300 degrees F (148.9 degrees C. for 1 to 2 seconds.

4. Which of the following microorganism survive at -9 to -17 degree C?
A. Salmonella
B. Staphylococci
C. Bacilli
D. Clostridium
Answer: A
Clarification: Species of Salmonella survive for longer periods of time at -9 to -17 degree C which is unlike the situation in which microbial count of most frozen foods decreases during storage.

5. Which of the following microorganism is eliminated in canned foods?
A. Mycobacterium tuberculosis
B. Coxiella burnetii
C. Clostridium botulinum
D. Lactobacillus
Answer: C
Clarification: The most important organism to be eliminated in canned foods is the spore forming anaerobe Clostridium botulinum, which is capable of producing a very potent lethal toxin.

6. Phosphatase enzyme present in milk is destroyed in which of the following processes?
A. Sterilization
B. Canning
C. Dehydration
D. Pasteurization
Answer: D
Clarification: Phosphatase is an enzyme present in raw milk and in many tissues which are destroyed by adequate pasteurization.

7. Jellies and jams are rarely affected by bacterial action.
A. True
B. False
Answer: A
Clarification: Jellies and jams are rarely affected by bacterial action because of high sugar content. However it is uncommon to find mold growth on the surface of jelly which has been exposed to air.

8. Which chemical is used to inhibit mold growth in bread?
A. benzoic acid
B. nitrates
C. sorbic acid
D. lactic acid
Answer: C
Clarification: Sorbic acid and propionic acid are used to inhibit mold growth in bread. They are organic in nature.

9. Acetic acid and lactic acid are used for __________________
A. curing meats
B. preservation of color
C. preservation of pickles
D. inhibiting mold growth
Answer: C
Clarification: Foods prepared from fermentation processes,e.g., sauerkraut, pickles, and silage for animals are preserved mainly by acetic, lactic and propionic acids produced during the microbial fermentation.

10. Which of the following method is used for treatment of water used for the depuration of shellfish?
A. Chemicals
B. Radiation
C. Low temperature
D. Osmotic pressure
Answer: B
Clarification: Radiations are used in the food industry, control of surface growth on bakery products, sanitation of equipment and treatment of water used for the depuration (cleansing) of shellfish.

.

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.

.