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.

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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.

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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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Microbiology Multiple Choice Questions on “Bacteria Cultivation – Bacteriological Media”.

1. Which of the following is a characteristic of beef extract?
A. product resulting from the digestion of proteinaceous materials
B. aqueous extract of lean beef tissue
C. aqueous extract of yeast cells
D. complex carbohydrate obtained from certain marine algae
Answer: B
Clarification: Beef extract, a complex raw material used as ingredient for preparing bacteriological media is an aqueous extract of lean beef tissue concentrated to a paste.

2. Which of the following is used as a solidifying agent for media?
A. Beef extract
B. Peptone
C. Agar
D. Yeast extract
Answer: C
Clarification: Agar is used as a solidification agent for media and is not considered a source of nutrient to the bacteria. Agar dissolved in aqueous solutions, gels when the temperature is reduced below 45 degrees Celsius.

3. Which of the following is a rich source of B vitamins?
A. Peptone
B. Yeast extract
C. Beef extract
D. Agar
Answer: B
Clarification: Yeast extract which is an aqueous extract of yeast cells is a very rich source of the B vitamins and it also contains apart from it organic nitrogen and carbon compounds.

4. The isolation of gonorrhea-causing organism, Neisseria gonorrhoeae by the use of certain antibiotics in media is an example of which of the following?
A. Selective media
B. Differential media
C. Enriched media
D. Assay media
Answer: A
Clarification: The isolation of gonorrhea-causing organism, Neisseria gonorrhoeae, from a clinical specimen is facilitated by the use of media containing certain antibiotics; these antibiotics do not affect N.gonorrhoeae but do inhibit the growth of contaminating bacteria. This is an example of selective media as it allows the growth of only a particular microorganism.

5. Nutrient broth, a liquid media contains beef extract and peptone respectively in how much amounts?
A. 0.2%, 0.4%
B. 0.1%, 0.6%
C. 0.3%, 0.5%
D. 0.7%, 0.3%
Answer: C
Clarification: Nutrient broth which is the most widely used media in general bacteriological work, contains 0.3 percent beef extract and 0.5 percent peptone. It may also contain if required 0.8 percent NaCl to maintain the salt concentration.

6. Which of the following instrument is used for sterilizing the media after it has been prepared?
A. Autoclave
B. Laminar Air Flow Chamber
C. Inoculum Needle
D. Incubator
Answer: A
Clarification: Autoclave is a type of pressure cooker which has steam at 121.5 degree Celsius and under 15 psi pressure. This steam kills all the microbes present in the media and sterilizes it.

7. Colony formation can be observed in liquid media broth.
a)True
B. False
Answer: B
Clarification: If microbial growth is found in liquid media, then the media shows turbidity but no colony formation can be observed. But in solid media microbial growth can be observed by colony formation as the media is already turbid due to the presence of agar powder.

8. Which of the following is a Complex media for fungal growth?
A. Nutrient broth
B. Luria-Bertani media
C. Potato Dextrose Agar(PDA. media
D. Mac Conkey Agar media
Answer: C
Clarification: Complex media is a chemically undefined media where the exact composition is not known. For fungal growth, complex media used is Potato Dextrose Agar(PDA. media.

9. Which of the following are functions of Maintenance Media?
A. used for assay of vitamins, amino acids
B. used for determining the bacterial content
C. used for determining the type of growth produced by bacteria
D. used for the maintenance of the viability and physiological characteristics
Answer: D
Clarification: Satisfactory maintenance of the viability and physiological characteristics of culture over time may require a medium different from that which is optimum for growth. Prolific, rapid growth may also be associated with rapid death of the cells at the end of the growth phase. Thus, a maintenance medium is required then.

10. Which of the following bacteria requires nicotinic acid as a growth factor in their media?
A. Proteus vulgaris
B. Nitrosomonas sp.
C. E. coli
D. Leuconostoc mesenteroides
Answer: A
Clarification: Proteus vulgaris require nicotinic acid as a growth factor in their media along with glucose as a carbon source and also Ammonium Chloride.

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Microbiology Multiple Choice Questions on “Microbial Metabolism – Process of Protein Synthesis”.

1. The amino acids for protein synthesis is activated by the enzyme ______________
A. rna synthetase
B. aminoacyl-tRNA synthetase
C. tRNA synthetase
D. aminoacyl-mRNA synthetase
Answer: B
Clarification: The first step in protein synthesis is the activation of amino acids. The amino acids are activated by amino-acid activating enzymes called aminoacyl-tRNA synthetase.

2. The activation of amino acids requires energy.
A. True
B. False
Answer: A
Clarification: The activation of amino acids for protein synthesis requires energy in the form of ATP. There is a specific activating enzyme for each kind of amino acid.

3. tRNA has a _______________ structure.
A. strand-like
B. ball-like
C. clover-leaf
D. leaf-like
Answer: C
Clarification: tRNA has a clover-leaf structure.The tRNA functions in protein synthesis to carry amino acids to, and recognize codons in, mRNA.

4. Transfer RNA is a single chain of ___________ nucleotides.
A. 340
B. about 100
C. about 80
D. 200
Answer: C
Clarification: Transfer RNA is a single chain of about 80 nucleotides that is folded back upon itself and held in a clover-leaf arrangement by means of hydrogen bonding due to complementary base pairing.

5. The terminal sequence of nucleotides in all tRNA is __________
A. ACC
B. UGC
C. UCC
D. AGC
Answer: A
Clarification: The terminal sequence of nucleotides is adenylic-cytidylic-cytidilic (ACC. and is found in all tRNA. The amino acid to be carried is linked to the terminal nucleotide containing adenine.

6.The tRNA carries amino acids to the ____________
A. rRNA
B. mRNA
C. sRNA
D. hnRNA
Answer: B
Clarification: The tRNA carries amino acid to the mRNA attached to the surface of the ribosome. Here the amino acid is added to a growing polypeptide chain.

7. The ribosome of E.coli is made up of which two subunits?
A. 60S and 40S
B. 60S and 30S
C. 50S and 40S
D. 50S and 30S
Answer: D
Clarification: The ribosomes of E.coli have been studied extensively and have been found to consist of two subunits. The larger subunit is a 50S particle, while the smaller unit is a 30S particle.

8. S,the Svedberg unit is a measure of ____________________________
A. the size of the ribosome
B. the composition of the ribosome
C. how fast a particle sediments during ultracentrifugation.
D. how the subunits combine in a ribosome
Answer: C
Clarification: S is the Svedberg unit, a measure of how fast particle sediments during ultracentrifugation. The association of a 30S and 50S subunit to form a 70S ribosome shows that the sedimentation behavior of the 70S ribosome is not a simple addition of the units of the smaller particles.

9. Which of the following statement is correct?
A. The ribosome binds to any end of a mRNA
B. CTP is required for activation of amino acids
C. Activated amino acids bind to the 5’ end of a respective tRNA molecule
D. The protein chain dissociates from the last tRNA molecule
Answer: D
Clarification: The amino group of the amino acid on the second tRNA reacts with the active terminal carboxyl group on the amino acid of the first tRNA to form a dipeptide; the first tRNA is then released. The process is continued till the peptide chain is complete. Termination takes place at one of the nonsense codons and the chain dissociates from the last tRNA molecule.

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Microbiology Multiple Choice Questions on “Algae – Characteristics”.

1. Chlorophyll d is present in the members of _____________________
A. Xanthophycophyta
B. Phaeophycophyta
C. Rhodophycophyta
D. Chrysophycophyta
Answer: C
Clarification: Chlorophyll d is present only in the members of Rhodophycophyta. There are five chlorophylls a, b, c, d, e which are found in different organisms.

2. Fucoxanthin pigment is present in _______________
A. Rhodophycophyta
B. Xanthophycophyta
C. Phaeophycophyta
D. Chlorophycophyta
Answer: C
Clarification: Fucoxanthin is present in Phaeophycophyta and gives it its characteristic colour brown. Other pigments like carotene and chlorophyll a and c are also present along with fucoxanthin.

3. Phycoerythrin pigment is present in which algal division?
A. Xanthophycophyta
B. Rhodophycophyta
C. Chrysophycophyta
D. Phaeophycophyta
Answer: B
Clarification: Phycoerythrin and phycocyanin are biloproteins present in Rhodophycophyta. They are also present in cryptomonads.

4. Chrysolaminarin is the reserved food of ___________________
A. Chlorophycophyta
B. Phaeophycophyta
C. Xanthophycophyta
D. Bacillariophycophyta
Answer: C
Clarification: Chrysolaminarin is the reserved food of Xanthophycophyta which is the yellow-green algae along with oils.

5. Cell walls of diatoms are impregnated with _____________
A. chitin
B. cellulose
C. starch
D. silica
Answer: D
Clarification: Cell walls of diatoms are impregnated with silica, making them thick and very rigid; they are often delicately sculptured with intricate designs characteristic of the species or variety.

6. Chloroplasts of algae embedded in the midst of the cytoplasm is known as ________________
A. parietal
B. asteroidal
C. central
D. peripheral
Answer: B
Clarification: The chloroplasts may be massive structures situated near the wall which are known as parietal or embedded in the midst of the cytoplasm which are known as asteroidal.

7. Carotenes are oxygenated derivatives of hydrocarbons.
A. True
B. False
Answer: B
Clarification: Carotenes are linear, unsaturated hydrocarbons, and xanthophylls are oxygenated derivatives of these.

8. Two lateral flagella are present in which of the following groups of algae?
A. Rhodophycophyta
B. Xanthophycophyta
C. Phaeophycophyta
D. Bacillariophycophyta
Answer: C
Clarification: Phaeophycophyta or the brown algae consists of two lateral flagella. Dinoflagellate or cryptomonads also consists of two lateral flagella.

9. Gullet is present in which algae?
A. Euglenoids
B. Golden algae
C. Dinoflagellates
D. Green algae
Answer: A
Clarification: Euglenoids or Euglenophycophyta contain gullet which is anteriorly present. It contains 1, 2 or 3 equal or slightly apical flagella.

10. Which of the following are water-soluble pigments?
A. chlorophyll
B. biloproteins
C. carotenoids
D. fucoxanthin
Answer: B
Clarification: Biloproteins or phycobilins are water-soluble pigments whereas chlorophylls and carotenoids are lipid-soluble.

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