Category: MICROBIOLOGY Objective Questions

Microbiology Multiple Choice Questions on “Physical Agents”.

1. Among the following which one is the most effective method of killing microorganisms?
A. High temperature
B. Low temperature
C. High temperature, high moisture
D. Low temperature, high moisture
Answer: C
Clarification: High temperatures combined with high moisture are one of the most effective methods of killing microorganisms. It is important to distinguish between dry heat and moist heat in any procedure for microbial control.

2. How much time is required by spores of Clostridium botulinum to be killed by moist heat at 1200C?
A. 2 hours
B. 4 to 20 minutes
C. 24 hours
D. 6-7 hours
Answer: B
Clarification: Spores of Clostridium botulinum are killed in 4 to 20 minutes by moist heat at 1200C, whereas a 2 hours exposure to dry heat at the same temperature is required.

3. Vegetative cells are much more sensitive to heat than are spores.
A. True
B. False
Answer: A
Clarification: Vegetative cells are much more sensitive to heat than the spores because of the higher level of water activity in the vegetative cells.

4. Which of the following conditions are required for the determination of thermal death time?
A. temperature is varied
B. time is fixed
C. temperature is fixed and time is varied
D. temperature is fixed and time is not selected
Answer: C
Clarification: In thermal death time, the temperature is selected as the fixed point and the time is varied. It refers to the shortest period of time to kill a suspension of bacteria or spores at a prescribed temperature and under specific conditions.

5. Which of the following apparatus is used to provide steam under regulated pressure?
A. autoclave
B. laminar air flow
C. incubator
D. hot oven
Answer: A
Clarification: The laboratory apparatus designed to use steam under regulated pressure is called an autoclave. It is essentially a double-jacketed steam chamber that can maintain steam under pressure and temperature.

6. The general pressure at which the autoclave is operated is ___________
A. 5 Psi
B. 20 Psi
C. 15 Psi
D. 40 Psi
Answer: C
Clarification: Generally the autoclave is operated at a pressure of approximately 15 Psi at 121.50C. It is not the pressure that kills the organisms but the temperature of the steam.

7. Some amount of air is also essential inside the chamber of the autoclave.
A. True
B. False
Answer: B
Clarification: In the operation of an autoclave it is absolutely essential that the air in the chamber be completely replaced by saturated steam. If air is present, it will reduce the temperature obtained within the chamber substantially below.

8. Which of the following methods is used for killing microorganisms of only certain types and not all microorganisms?
A. Pasteurization
B. Incineration
C. Boiling water
D. Fractional Sterilization
Answer: A
Clarification: In pasteurization, milk, cream, and certain alcoholic beverages are subjected to a controlled heat treatment that kills microorganisms of certain types but does not destroy all organisms.

9. Which of the following instruments is used to perform tyndallization?
A. Autoclave
B. Steam Arnold
C. Gas oven
D. Incubator
Answer: B
Clarification: For tyndallization or fractional sterilization the apparatus used is the Steam Arnold however an autoclave can also be used if a free-flowing steam is used.

10. Which of the following actions occur due to low temperature?
A. coagulation of proteins
B. death of microorganisms
C. rate of metabolism is reduced
D. denatures proteins
Answer: C
Clarification: Temperatures below the optimum for growth depresses the rate of metabolism and if the temperature is sufficiently low, growth and metabolism ceases. Low temperature are also useful for the preservation of cultures.

11. Which of the following are resistant to desiccation?
A. gonococci
B. streptococci
C. meningococci
D. bacillus
Answer: B
Clarification: Streptococci are much more resistant to dessication, some survive weeks after being dried but species of Gram-negative cocci are very sensitive to dessication.

12. Passage of water from a low solute concentration into the cell is referred to as ______________
A. plasmoptysis
B. plasmolysis
C. isotonic
D. hypertonic
Answer: A
Clarification: The passage of water from a low solute concentration into the cell is termed plasmoptysis. The pressure built up within the cell as a result of this water intake is termed osmotic pressure.

13. Which of the following radiations have the energy to knock electrons away from molecules and ionize them?
A. Non-ionizing radiations
B. Acoustic radiations
C. Subatomic particles
D. Ionizing radiations
Answer: D
Clarification: Gamma rays and x-rays are called ionizing radiations because they have enough energy to knock electrons away from molecules and ionize them. When such radiations pass through cells, they create free hydrogen radicals, hydroxyl radicals and some peroxides which causes intracellular damage.

14. Wavelengths around ___________ have the highest bactericidal efficiency.
A. 150 Å
B. 3900 Å
C. 2650 Å
d)1500 Å
Answer: C
Clarification: The ultraviolet portion of the spectrum includes all radiations from 150 to 3900 Å. Wavelengths around 2650 Å have the highest bactericidal efficiency.

15. Which of the following inhibits DNA replication?
A. cathode rays
B. UV light
C. x-rays
D. gamma rays
Answer: B
Clarification: Ultraviolet light is absorbed by many cellular materials but most significantly by the nucleic acids where it does the most damage. Pyrimidine dimers are formed due to which DNA replication is inhibited and mutations can result.

16. Which material is used for the Berkefeld filter?
A. diatomaceous earth
B. asbestos pad
C. porcelain
D. sintered glass disks
Answer: A
Clarification: Filters can remove microorganisms from liquids or gases. The Berkefeld filter is made up of diatomaceous earth.

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Microbiology Multiple Choice Questions on “Microbial Flora of Fresh Foods”.

1. Which of the following organism occurs on the skin of fresh poultry?
A. pseudomonads
B. staphylococci
C. micrococci
D. enterococci
Answer: A
Clarification: Pseudomonads constitute the major contaminants on the skin of freshly dressed poultry.

2. What is the pH of the bananas?
A. 2.3
B. 5.0
C. 7.0
D. 12.0
Answer: B
Clarification: The pH of fruits is relatively acid ranging from 2.3 for lemons to 5.0 for bananas. This restricts bacterial growth but does not retard fungal growth.

3. Raw milk of good sanitary quality will develop sweet flavour.
A. True
B. False
Answer: B
Clarification: Raw milk of good sanitary quality will develop a clean, sour flavour. This change is brought about mainly by Streptococcus lactis and S.cremoris.

4. At what temperature pasteurization of milk takes place?
A. 650 C
B. 370 C
C. 62.80 C
D. 450 C
Answer: C
Clarification: The holding method of pasteurization exposes milk to a temperature of 62.80 C for 30 mins.

5. Which among the following is a gas producer organism?
A. Streptococcus lactis
B. Lactobacillus fermentum
C. Micrococcus luteus
D. Clostridium butyricum
Answer: D
Clarification: Clostridium butyricum causes fermentation of lactose with accumulation of gas. The gas may be a mixture of carbon dioxide and hydrogen or only carbon dioxide in case of yeast fermentation.

6. Which among the following group of microorganisms are found in the ducts of cow’s mammary glands?
A. Coliforms
B. Lactobacilli
C. Micrococci
D. Microbacteria
Answer: C
Clarification: Micrococci such as Micrococcus luteus, Micrococcus varians are found in the ducts of cow’s mammary glands and dairy utensils. They are acid producers and are weakly proteolytic.

7. The coloration of the milk is caused by which of the following organism?
A. Pseudomonas sp.
B. Bacillus sp.
C. Penicillium sp.
D. Streptococcus sp.
Answer: A
Clarification: Pseudomonas sp. may produce coloration of milk. End products of proteolysis may impart abnormal flavor or odor to the milk.

8. In which of the following biochemical types of microorganisms a slime layer or capsule is formed on the cells?
A. Acid producers
B. Gas producers
C. Ropy or stringy fermentation
D. Proteolytic
Answer: C
Clarification: In Ropy or stringy fermentation, organisms synthesize a viscous polysaccharide material that forms a slime layer or capsule on the cells. They include Alcaligenes viscolactis, Enterobacter aerogenes, etc.

9. Tuberculosis brucellosis is caused by the pathogen from an infected cow.
A. True
B. False
Answer: A
Clarification: Pathogen from infected cow are transmitted through milk to humans or cow and causes tuberculosis brucellosis, mastitis.

10. Which of the following type of spoilage occurs in fresh meat?
A. Souring
B. Greening
C. Putrefaction
D. Moldy
Answer: C
Clarification: Fresh meat is spoiled by putrefaction and is caused by Alcaligenes, Clostridium, Proteus vulgaris etc. In putrefaction, the protein foods are degraded by proteolytic microorganisms to give amino acids, amines, ammonia and hydrogen sulphide.

11. Spoilage of bread is caused by which of the following microorganism(s)?
A. Saccharomyces
B. Rhizopus
C. Leuconostoc
D. Pseudomonas
Answer: B
Clarification: Moldy and ropy type of spoilage occurs in bread which are caused by Rhizopus nigricans, Penicillium, Aspergillus niger and Bacillus subtilis.

12. The thermophilic anaerobe spoilage of low and medium acid canned products are caused by _____________
A. Bacilllus stearothemophilus
B. Clostridium thermosaccharolyticum
C. Bacillus thermoacidurans
D. Clostridium sporogenes
Answer: B
Clarification: Thermophilic anaerobe spoilage of low and medium acid canned products such as corn, peas, spinach are caused by Clostridium thermosaccharolyticum. It can swells and may burst.

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Microbiology Question Bank focuses on “Infection Process – Events in Infection Following Penetration”.

1. Gas gangrene is caused by which of the following microorganisms?
A. Staphylococcus aureus
B. Clostridium perfringens
C. Pseudomonas aeruginosa
D. E.coli
Answer: B
Clarification: Anaerobic bacteria, Clostridium perfringens, causes wound infection gas gangrene.

2. The characteristic lesion, abscess caused by Staphylococcus aureus is a type of non-localized infection.
A. True
B. False
Answer: B
Clarification: The characteristic lesion, abscess caused by Staphylococcus aureus, is a walled-off cavity in the tissues containing the staphylococci, numerous white blood cells, etc. This is a type of localized infection.

3. Which of the following condition is false for tissue invasion by C.perfringens?
A. anaerobic condition of the wound
B. production of large amounts of hydrogen gas
C. production of small amounts of hydrogen gas
D. release of toxins
Answer: C
Clarification: Production of large amounts of hydrogen gas by the bacteria contributes to the rapidity of tissue invasion.

4. Amputation is the only way to stop the spread of C.perfringens to the rest of the body.
A. True
B. False
Answer: A
Clarification: Amputation of an affected limb is often the only way to stop the spread of C.perfringens to the rest of the body.

5. What is the shape of the lymph nodes?
A. tubular
B. circular
C. cuboidal
D. ovoid
Answer: D
Clarification: Lymph nodes are ovoid structures ranging in size from one to several millimeters and are widely distributed throughout the body.

6. Lymph enters a lymph node by several _________________
A. lymphatic trunks
B. lymphatic vessels
C. lymphatic ducts
D. arteries
Answer: B
Clarification: Lymph enters a lymph node by any of several lymphatic vessels, passes through the lymph node along tortuous, winding channels, and emerges via a single efferent lymph vessel.

7. Which microbe causes the disease erysipelas?
A. S. pyogenes
B. C. perfringens
C. Pseudomonas aeruginosa
D. E.coli
Answer: A
Clarification: Erysipelas, an inflammatory disease of the skin is caused by S. pyogenes. The painful lesions are spread by invasion of the lymphatic system of the subepidermal tissue.

8. Which of the following is not the characteristic of a bubo?
A. inflamed
B. sore when infected
C. small
D. free from bacteria
Answer: C
Clarification: The lymph node removes nearly all of the bacteria that enters it, and it may become inflamed, enlarged, and sore when infected and in this condition it is sometimes called a bubo.

9. Where does Neisseria meningitidis reach after entering the body?
A. kidney
B. intestine
C. nasopharynx
D. meninges
Answer: D
Clarification: Neisseria meningitidis present in the nasopharynx can reach the meninges (membranes that cover the brain and spinal corD. by means of transient bacteremia.

10. Which of the following microorganism can cause acute renal failure?
A. Leptospira
B. Salmonella typhi
C. Neisseria meningitidis
D. Bacillus anthracis
Answer: A
Clarification: By means of bacteremia, spirochetes of the genus Leptospira can reach the kidneys, where they may eventually cause acute renal failure.

11. Which of the following disease is caused by the pathogen directly infecting the lymphatic system?
A. meningitis
B. typhoid fever
C. renal failure
D. anemia
Answer: B
Clarification: In typhoid fever, Salmonella typhi after penetrating through the epithelial cells, enter the lymphatic system, and reach the mesenteric lymph nodes.

12. Which of the following disease is an example of septicemic infection?
A. typhoid fever
B. meningitis
C. anthrax
D. renal failure
Answer: C
Clarification: Anthrax is an example of septicemic infection in which the number of Bacillus anthracis organisms may often exceed the number of erythrocytes in the blood.

To practice Microbiology Question Bank, .

Microbiology Multiple Choice Questions on “Bacteria Cultivation – Nutritional Requirements”.

1. The organisms which can use reduced inorganic compounds as electron donors are known as _________
A. chemotrophs
B. organotrophs
C. lithotrophs
D. phototrophs
Answer: C
Clarification: Organisms that can use reduced inorganic compounds as electron donors are termed as lithotrophs. Some organisms which use organic compounds as electron donors are called organotrophs.

2. Which of the following is the nutritional characterization of Escherichia coli?
A. Chemotrophic
B. Organotrophic
C. Autotrophic
D. Chemotrophic, Organotrophic, Heterotrophic
Answer: D
Clarification: Escherichia coli are chemotrophic, organotrophic, and heterotrophic organisms. This means they rely on chemical compounds for their energy and uses organic compounds as electron donors. They also require organic compounds as their carbon source and are hence heterotrophic.

3. Which of the following amino acids require sulphur for their synthesis?
A. tryptophan
B. methionine
C. cystine
D. methionine and cystine
Answer: D
Clarification: Sulphur is needed for synthesis of certain amino acids like methionine and cystine. Some bacteria require organic sulphur compounds, some are capable of utilizing inorganic sulphur compounds and some can even use elemental sulphur.

4. Phosphorus is essential component of __________
A. teichoic acid
B. nucleotides
C. phospholipids
D. teichoic acid, nucleotides, phospholipids
Answer: D
Clarification: Phosphorus, usually supplied in the form of phosphate, is an essential component of nucleotides, nucleic acids, phospholipids, teichoic acids, and other components.

5. Which of the following are trace elements?
A. Potassium ion
B. Sodium ion
C. Copper ion
D. Magnesium ion
Answer: C
Clarification: Trace elements are those elements that are needed at very low concentrations such as Zinc ion, Copper ion, Manganese ion, Nickel ion, Cobalt ion, Boron ion, Molybdenum ion. They always occur as contaminants of other components of culture media in amounts sufficient to support bacterial growth.

6. Which of the following ions are cofactors for various enzymes?
A. Potassium ion
B. Iron ion
C. Magnesium ion and Iron ion
D. Calcium ion
Answer: C
Clarification: Among the trace elements, iron ion, magnesium ion, zinc ion, manganese ion and copper ion are known to be cofactors for various enzymes.

7. ”Red extreme halophiles”, are members of the archaebacterial which cannot grow with less than 12 to 15 percent NaCl.
A. True
B. False
Answer: A
Clarification: Most bacteria do not require Na ion, but certain marine bacteria, cyanobacteria and photosynthetic bacteria do require it. For those members of the archaeobacteria known as the “red extreme halophiles”, the requirement is astonishing: they cannot grow with less than 12 to 15 percent NaCl. They require this high level of NaCl for maintenance of the integrity of their cell walls and for the stability and activity of certain of their enzymes.

8. Which of the following are functions of water in the culture medium?
A. nutrients must be in aqueous solution
B. cofactor of enzymes
C. provides resistance to sudden transient temperature changes
D. it is a chemical reactant, nutrients must also be present in aqueous solution and provide resistance to sudden temperature changes
Answer:d
Clarification: In the case of bacteria, all nutrients must be in aqueous solution before they can enter the cells. The high specific heat of water provides resistance to sudden, transient temperature changes in the environment. Water is also a chemical reactant, being required for the many hydrolytic reactions carried out by a cell.

9. Chromatium okenii uses which of the following compound as electron donor?
A. Hydrogen sulphide
B. Fatty acids
C. Alcohol
D. Succinate
Answer: A
Clarification: Chromatium okenii are photolithotrophs i.e., they are phototrophic bacteria that uses inorganic compounds as their source of electrons. They use Hydrogen Sulphide as its electron donor, oxidizing it to elemental sulphur.

10. Which of the following bacteria can grow both as chemolithotrophs or as chemoorganotrophs?
A. Nitrosomonas sp.
B. Pseudomonas pseudoflava
C. Rhodospirillum rubrum
D. Chromatium okenii
Answer: B
Clarification: Pseudomonas pseudoflava can grow either as chemolithotrophs or chemoorganotrophs. They can use either the organic compound glucose or the inorganic compound hydrogen as its source of electrons.

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Microbiology Multiple Choice Questions on “Microbial Metabolism – Transcription and Translation of Genetic Information”.

1. Translation takes place before transcription.
A. True
B. False
Answer: B
Clarification: According to the central dogma of molecular genetics, the first step is DNA replication, the second is a transcription and the last step is translation.

2. Which of the following bacteria can synthesize all of the amino acids required for protein synthesis?
A. E.coli
B. Lactobacillus bravis
C. Saccharomyces cerevisiae
D. Bacillus subtilis
Answer: A
Clarification: Microorganisms differ widely in their ability to synthesize amino acids like E.coli can synthesize all of the amino acids required for protein synthesis, whereas lactic acid bacteria cannot.

3. RNAase is a single polypeptide chain of __________ amino acid residues.
A. 2
B. 350
C. 4
D. 124
Answer: D
Clarification: RNAase is a single polypeptide chain of 124 amino acid residues; it is folded, bent and twisted into a globular shape in its active form.

4. Protein synthesis in bacteria takes place on which of the following organelles?
A. Endoplasmic Reticulum
B. Golgi body
C. Ribosomes
D. Mitochondria
Answer: C
Clarification: Protein synthesis in bacteria takes place on the ribosomes, which are larger RNA-protein particles in the cytoplasm of the bacterial cell.

5. Which of the following RNA constitutes 90 percent of the total cellular RNA?
A. rRNA
B. tRNA
C. mRNA
D. hnRNA
Answer: A
Clarification: Ribosomal RNA (rRNA. constitutes about 90 percent of the total cellular RNA and this is important from all other types of RNA.

6. The synthesis of polynucleotide chain of mRNA is catalyzed by the enzyme _____________
A. RNA helicase
B. RNA polymerase
C. DNA polymerase
D. DNA helicase
Answer: B
Clarification: The synthesis of polynucleotide chain of mRNA is catalyzed by the enzyme RNA polymerase. The process in which a single-stranded mRNA is synthesized complementary to one DNA strand is called transcription.

7. Which of the following is responsible for the initiation of RNA polymerase activity?
A. initiation site
B. promoter region
C. sigma factor
D. rho factor
Answer: C
Clarification: In bacteria, the initiation of RNA polymerase activity at the initiation site is due to an initiation factor called the sigma factor, which is a component of the enzyme.

8. Rho factor is a dimeric protein factor.
A. True
B. False
Answer: B
Clarification: Rho factor is a tetrameric protein factor that binds to RNA polymerase and promotes its termination. When transcription has been completed, rho dissociates from the RNA polymerase-DNA complex.

9. The following code codes for which of the amino acid respectively?
AUG and GUG
A. Phenylalanine, tyrosine
B. Methionine, valine
C. Methionine, alanine
D. Lysine, valine
Answer: B
Clarification: Three base triplets form a codon that codes for an amino acid. Thus AUG codes for methionine and GUG codes for Valine. AUG and GUG are both initiating codons for translation.

10. Which of the following are non-sense codons?
A. AUG
B. GUG
C. UAA
D. UCU
Answer: C
Clarification: UAA, UAG and UGA are polypeptide-chain-terminating codons and are called non-sense codons.

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Microbiology Multiple Choice Questions on “Algae Biological and Economic Importance”.

1. Alginic acid is obtained from ______________
A. brown algae
B. red algae
C. yello-green algae
D. golden algae
Answer: A
Clarification: Alginic acid and its salts are obtained from the walls of brown algae, where they may represent as much as 25 percent of the dry weight. Laminaria, Fucus are some of the species producing this compound.

2. Agar is obtained from the algal species of _______________
A. Chondrus
B. Gigartina
C. Gelidium
D. Laminaria
Answer: C
Clarification: Species of Gelidium and Gracilaria belonging to red algae are extensively used for obtaining agar.

3. Carrageenan is used as a ______________
A. emulsifier
B. solidifying agent
C. binder
D. emulsifier and binder
Answer: D
Clarification: Carrageenan has been used as a stabilizer or emulsifier in foods such as ice-cream and other milk products. It is also used as a binder in toothpaste or in pharmaceutical products, as well as an agent in ulcer therapy.

4. The famous Japanese dish sushi is made with the help of the red algae named ____________
A. Nemalion
B. Porphyra
C. Chondrus
D. Eucheuma
Answer: B
Clarification: Porphyra is used as a food in Japan, where it is called “nori” and is usually processed into dried sheets. Nori is commonly toasted over a flame and sprinkled in soup or rice, or it is rolled around flavoured rice with fish or vegetables to make sushi.

5. Which among the following is a pathogenic algae for humans?
A. Prototheca
B. Chlorella
C. Cephaleuros
D. Acanthopeltis
Answer:a
Clarification: Prototheca has been found to be a probable pathogen of humans. It has been found in systemic and subcutaneous infections, as well as in bursitis.

6. Algae are known as primary producers.
A. True
B. False
Answer: A
Clarification: Algae form the base or beginning of most aquatic food chains because of their photosynthetic activities and are therefore called primary producers of organic matter.

7. Agar and carrageenan are polymers of _________________
A. glucose
B. phosphoric acid
C. starch
D. galactose
Answer: D
Clarification: Agar and carrageenan are polymers of galactose, or galactose-containing compounds, with sulfated groups. Agar and carrageenan are both called sulfated galactans.

8. Which of the following species are important for cervical dilation?
A. Laminaria japonica
B. Gracilaria
C. Chondrus
D. Gonyaulax catenella
Answer: A
Clarification: The stipe of the brown alga Laminaria japonica may be used by the physicians for cervical dilation and/or softening of the cervix (for example, in performing an abortion or placing a radium implant).

9. Which of the following algae continues to be a significant food in China?
A. brown algae
B. green algae
C. red algae
D. yellow algae
Answer: C
Clarification: Red algae continue to be significant food in China. Such algae have been a food staple and delicacy for the Chinese for thousands of years.

10. Which of the following species produces neurotoxin which causes the death of aquatic animals?
A. Chlorella
B. Gonyaulax
C. Prototheca
D. Cephaleuros
Answer: B
Clarification: It is known that certain dinoflagellates belonging to the genera Gymnodinium and Gonyaulax cause death of aquatic animals by producing a high molecular weight neurotoxin.

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