Category: MICROBIOLOGY Objective Questions

Microbiology Questions and Answers for Freshers focuses on “Quantitative Measurement of Bacterial Growth”.

1. Which of the following is an indirect method for measuring bacterial growth?
A. Cell count
B. Cell mass
C. Cell activity
D. Both Cell mass and Cell activity
Answer: C
Clarification: Cell activity is an indirect method for measuring bacterial growth by relating the degree of biochemical activity to the size of the population.

2. Which of the following instrument is used for the bacterial count?
A. Petroff-Hausser counting chamber
B. Microscope
C. Chemostat
D. Turbidostat
Answer: A
Clarification: Bacteria can be counted easily and accurately with the Petroff-Hausser counting chamber. This is a special slide accurately ruled into squares that are 1/400 mm2 in area. A suspension of unstained bacteria can be counted in the chamber, using a phase contrast microscope.

3. Which of the following method is used for a viable count of a culture?
A. Direct microscopic count
B. Plate-count method
C. Membrane-filter count
D. Plate-count method and membrane-filter count
Answer: D
Clarification: The main disadvantage of direct counting of cell numbers is that there is no way to determine whether the cells being counted are viable. To determine the viable count of culture, we must use a technique that allows viable cells to multiply, such as the plate-count method or membrane-filter method.

4. The number of bacteria per ml depends on the dilution of the sample.
A. True
B. False
Answer: A
Clarification: In the plate count method, the formula used is as follows:
Number of bacteria per ml = Number of colonies counted on plate X dilution of sample.
Thus number of bacteria directly depends on the dilution of sample.

5. Which of the following is the relationship between optical density and cell mass?
A. exponentially proportional
B. linearly proportional
C. inversely proportional
D. not related
Answer: B
Clarification: The photoelectric colorimeter used for measuring bacterial population, measures optical density (a function of light intensity) which is almost linearly proportional to cell mass.

6. How many cells present per milliliter in a bacterial culture can make the culture turbid?
a)1 cell
b)1000 cells
c)1 lakh cells
d)107-108 cells
Answer: D
Clarification: Bacteria in a suspension absorb and scatter the light passing through them so that a culture of more than 107 to 108 cells per milliliter appears turbid to the naked eye. Then a spectrophotometer or colorimeter can be used for turbidimetric measurements.

7. A dead cell does not contribute to turbidity in the culture medium.
A. True
B. False
Answer: B
Clarification: Both dead as well as living cells contribute to turbidity. However, turbidity cannot be measured for cultures grown in deeply colored media or cultures that contain suspended material other than bacteria.

8. Which of the following is a direct measurement of growth?
A. Determination of nitrogen content
B. Turbidimetric methods
C. Determination of Dry weight of cells
D. Measurement of a specific chemical change produced on a constituent of the medium
Answer: C
Clarification: To measure the dry weight of cells is the most direct approach for quantitative measurement. All others are indirect methods and is applicable only in special circumstances.

9. Which of the following method is used for enumeration of bacteria in vaccines and cultures?
A. Microscopic Count
B. Membrane filter
C. Plate count
D. Dry weight determination
Answer: A
Clarification: Membrane count is used for the enumeration of bacteria in vaccines and cultures. Even electronic enumeration is used in this application.

10. Colony-forming units per ml is the unit of _____________
A. Microscopic count
B. Electronic enumeration
C. Plate count
D. Turbidimetric measurement
Answer: C
Clarification: Since the plate count method is used in the enumeration of bacteria in milk, water, foods, soil, etc, the unit in which growth is measured is colony-forming units per ml as the bacteria forms colonies in the petri dish.

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Microbiology Interview Questions and Answers for Experienced people focuses on “World of Bacteria I – Anaerobic Gram-Negative Straight, Curved and Helical Rods”.

1. Bacteria belonging to the family Bacteriodaceae uses which of the following compounds as electron acceptors?
A. oxygen
B. inorganic sulphur
C. nitrate
D. phosphate
Answer: C
Clarification: Bacteriodaceae do not respire anaerobically by using inorganic sulphur as electron acceptors; some do respire anaerobically with nitrate or fumarate.

2. The organic acids produced by bacteria belonging to the family Bacteriadaceae is identified by?
A. distillation
B. gas chromatography
C. spectrophotometer
D. ion-exchange chromatography
Answer: B
Clarification: The bacteria of Bacteriadaceae differ in the kinds of organic acid end products they produce. The organic acids are identified by means of a gas chromatograph.

3. Which of the following genus of bacteria do not have a fermentative type of metabolism?
A. Bacteroides
B. Fusobacterium
C. Wolinella
D. Selenomonas
Answer: C
Clarification: Wolinella do not have a fermentative type of metabolism. They respire anaerobically with hydrogen or formate as electron donors and fumarate or nitrate as electron acceptors.

4. Which of the following possess peritrichous flagella?
A. Bacteroides
B. Anaerovibrio
C. Succinimonas
D. Fusobacterium
Answer: A
Clarification: Bacteroides are straight-rod shaped. They are nonmotile or motile by means of peritrichous flagella.

5. Propionate and acetate are produced as an end product of fermentation in which of the following bacteria?
A. Fusobacterium
B. Succinimonas
C. Wolinella
D. Anaerovibrio
Answer: D
Clarification: Anaerovibrio are slightly curved rod shaped bacteria that are motile by means of a single polar flagellum. They produce propionate and acetate as organic acid end products of the fermentation process.

6. Desulphuromonas can respire with elemental sulphur as the electron acceptor.
A. True
B. False
Answer: A
Clarification: Desuphuromonas is one genus of sulphur reducing bacteria that can respire with elemental sulphur as the electron acceptor. The other genera cannot use sulphur but can use sulphate, thiosulphate, or other oxidized sulphur compounds.

7. Veillonellaceae is the family of bacteria consisting of motile cocci.
A. True
B. False
Answer: B
Clarification: Veillonellaceae consists of nonmotile cocci, typically occurring in pairs, often with the adjacent sides flattened.

8. The violet pigement, violacein, is produced by which of the following bacterial genus?
A. Zymomonas
B. Gardnerella
C. Streptobacillus
D. Chromobacterium
Answer: D
Clarification: Chromobacterium are motile, rod-shaped organisms having the unusual property of forming violet colonies, due to a pigment called violacein. They can cause infections in humans and other mammals.

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Microbiology Multiple Choice Questions on “Protozoa – Reproduction”.

1. Which of the following type of fission takes place in flagellates?
A. longitudinal
B. right angle to the cell axis
C. transverse
D. cytoplasm protrudes from the aperture
Answer: A
Clarification: In flagellates, with the exception of the dinoflagellates, fission is longitudinal along the major body axis. Since the flagella themselves are incapable of division, they must be regenerated from the basal bodies.

2. Which of the following does not take place in transverse fission?
A. fission occurs at the right angle to the long cell axis
B. equatorial furrow appears
C. cytoplasm protrudes from the aperture
D. constriction occurs forming two daughter cells
Answer: C
Clarification: In transverse fission which is characteristic for ciliates, fission occurs at a right angle to the long axis of the cell. An equatorial furrow appears first which separates the surface cell layer into an anterior and a posterior half. A constriction follows, leading to the separation of two daughter cells.

3. During asexual binary fission the macronucleus divides by mitotic division.
A. True
B. False
Answer: B
Clarification: In ciliates, during asexual binary fission the diploid micronucleus divides normally by mitotic division. The macronucleus undergoes DNA synthesis and divides into two portions without the regular reduplication of the chromosomes(amitosis).

4. Plasmodium divides by which of the following method most commonly?
A. Binary fission
B. Multiple fission
C. Budding
D. Regeneration
Answer: B
Clarification: The malarial parasite, Plasmodium divides by the process of multiple fission where it is known as schizogony and serves to spread the parasite quickly in the host.

5. The swarming daughter cells possess special locomoter organelles like the parent cell.
A. True
B. False
Answer: B
Clarification: The swarming daughter cells differ from the parent cell not only in a lower degree of differentiation but also in the possession of special locomotor organelles.

6. Definite exogenous budding occurs in which of the following species of protozoa?
A. foraminifera
B. radiolaria
C. suctorians
D. heliozoa
Answer: C
Clarification: Definite exogenous budding is seen in suctorians when a portion or portions of an adult sessile suctorian bud from the parent, develop cilia and swim away.

7. When the gametes are morphologically alike, they are called ______________
A. isogametes
B. anisogametes
C. macrogametes
D. microgametes
Answer: A
Clarification: When the gametes (which develop from trophozoites) are morphologically alike, they are called isogametes. When they are unlike they are known as isogametes.

8. Long,slender bodies with an oval nucleus and capable of producing new infection are known as _________________
A. ookinetes
B. sporozoites
C. anisogametes
D. spermatozoa
Answer: B
Clarification: Anisogamy in Plasmodium vivax results in the formation of ookinetes or motile zygotes which give rise to a large number of sporozoites which are long, slender bodies with an oval nucleus and firm cuticle, capable of producing the new infection.

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Microbiology Multiple Choice Questions & Answers focuses on “Microbiological Assay of Antibiotics, Antifungal, Antiviral and Antitumour Antibiotics”.

1. Which of the following is the most accurate method for microbial assay of antibiotics?
A. Physical assay
B. Chemical assay
C. Biological assay
D. Chemical and biological assay
Answer: B
Clarification: Chemical-assay methods are generally more accurate and require less time than biological methods, but they are less sensitive, and caution must be used lest biologically inactive degradation products give misleading results.

2. The international unit of penicillin is defined by how much amount of International Standard?
A. 1 mg
B. 0.262 µg
C. 0.5988 µg
D. 0.5 mg
Answer: C
Clarification: The international unit of penicillin is the amount of activity produced under defined conditions by 0.5988 µg of the International Standard, which is a sample of pure benzyl-penicillin.

3. Zone of inhibition is observed in tube-dilution method.
A. True
B. False
Answer: B
Clarification: Small paper disks impregnated with known amounts of chemotherapeutic agents are placed upon the surface of an inoculated plate. So after incubation in disk-plate methods, a zone of inhibition around the disk indicates that the organism was inhibited by the drug.

4. Pigs respond dramatically to the addition of which of the following antibiotics to their diet?
A. aureomycin
B. terramycin
C. penicillin
D. oxytetracycline
Answer: D
Clarification: It has been suggested that pigs respond dramatically to the addition of oxytetracycline to their diet because the antibiotic inhibits the growth of Clostridium perfringens in their intestines and prevents a chronic but subclinical toxemia.

5. Which of the following antibiotic have a sparing effect on the B12 in the diet?
A. Streptomycin
B. Tetracycline
C. Anthramycin
D. Chloramphenicol
Answer: A
Clarification: Streptomycin may have a “sparing effect” on the B12 in the diet, making it available in greater quantities for utilization by the animals.

6. Antibiotics are not effective against plant pathogens.
A. True
B. False
Answer: B
Clarification: Some antibiotics are effective against plant pathogens and are attractive for the treatment of plant diseases. The extent of this practice is limited mainly by economic factors, i.e, the cost of the antibiotic.

7. Nystatin is produced from the strain _____________________
A. Streptomyces noursei
B. Streptomyces aureofaciens
C. Streptomyces kanamyceticus
D. Streptomyces fradiae
Answer: A
Clarification: Nystatin is an antifungal agent produced during fermentation by a strain of Streptomyces noursei.

8. Griseofulvin is useful in the therapy of nonsystemic fungal infections.
A. True
B. False
Answer: B
Clarification: Griseofluvin is used in the treatment of many superficial fungal infections of the skin and body surfaces and is also effective in the treatment of systemic mycoses.

9. Acycloguanosine is a nucleoside analog which is active against ___________________
A. Influenza A virus
B. HIV virus
C. Herpes virus
D. Influenza B virus
Answer: C
Clarification: Acycloguanosine is a nucleoside analog that is active against the herpes virus in animals. Its mode of action appears to be that of inhibition of nucleotide utilization.

10. Which of the following has its antiviral action attributed to the interference of protein synthesis?
A. Amantadine
B. Interferons
C. Acycloguanosine
D. 5’-iododeoxyuridine
Answer: B
Clarification: The antiviral action of interferons is attributed to interference of protein synthesis. Interferons is among the most promising chemotherapeutic agents for treating viral diseases.

11. Amantadine is very effective against influenza A virus.
A. True
B. False
Answer: A
Clarification: Amantadine is a low-molecular weight compound which is very effective against influenza A virus; it is not effective against influenza B. The incidence of influenza A infection is greatly reduced by the use of this drug.

12. Which of the following is effective in the control of tuberculosis in humans?
A. Nitrofurans
B. Nalidixic Acid
C. Sibromycin
D. Isoniazid
Answer: D
Clarification: Isonicotinic acid Hydrazide or Isoniazid has proved to be very useful in the control of tuberculosis in humans and is more effective when given alternately with streptomycin.

13. Anthramycin is which of the following type of antibiotic?
A. Antiviral
B. Antitumor
C. Antifungal
D. Antibacterial
Answer: B
Clarification: The anthramycin group (anthramycin, sibromycin, tomaymycin and neothramycin) is an example of potent antitumor agents. Their antitumor activity is directed towards DNA structure and function.

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Microbiology Multiple Choice Questions on “Industrial Uses of Molds”.

1. Gluconic acid is produced by which of the following molds?
A. Aspergillus niger
B. Rhizopus nigricans
C. Aspergillus terreus
D. Rhizopus oryzae
Answer: A
Clarification: Aspergillus niger is the producer organism for gluconic acid which is used as a pharmaceutical product, textiles, leather, or in photography.

2. Fermentation of rice is carried out by which of the following microorganisms?
A. bacteria
B. yeasts
C. molds
D. protozoa
Answer: C
Clarification: Molds are used for the fermentation of rice to produce a variety of oriental foods and food additives.

3. Penicillium chrysogenum is a better penicillin producing species.
A. True
B. False
Answer: A
Clarification: Fleming isolated the mold Penicillium notatum which yielded only a few units of penicillin per milliliter. So isloation of a better penicillin-producing mold species, Penicillium chrysogenum helped in increasing the yield.

4. Which of the following techniques is used to improve penicillin production?
A. fed-batch fermentation
B. submerged-culture technique
C. continuous fermentation
D. batch fermentation
Answer: B
Clarification: Penicillin production can be improved by the development of the submerged culture technique i.e., cultivation of the mold in large volumes of liquid medium through which sterile air is forced.

5. Which of the following product acts as a substrate for the production of citric acid?
A. molasses
B. corn-steep liquor
C. barn
D. oyabeen meal
Answer: A
Clarification: Many sugars may serve as the substrate for the production of citric acid, however, molasses is generally used.

6. Which of the following enzymes is used to hydrolyze starch to dextrin?
A. invertase
B. pectinase
C. amylase
D. protease
Answer: C
Clarification: Amylases hydrolyze starch to dextrin and sugars and are used in preparing adhesives, clarifying fruit juices, manufacturing pharmaceuticals etc.

7. Which of the following enzyme is used in the process of bating?
A. invertase
B. pectinase
C. amylase
D. protease
Answer: D
Clarification: Proteases are used for bating i.e. treatment of hides to provide a finer texture and grain in leather processing.

8. Paper, glass beads can be used to immobilize enzymes.
A. True
B. False
Answer: A
Clarification: A variety of substances including paper, wood chips, ceramic, glass beads, and ion-exchange resins have been used to immobilize enzymes.

9. Invertase causes hydrolysis of ___________
A. starch
B. sucrose
C. proteins
D. pectins
Answer: B
Clarification: Invertase hydrolyzes sucrose to form glucose and fructose (invert sugar). It is widely used in candy making and the production of noncrystallizable syrups from sucrose.

10. Rhizopus nigricans produces which of the following products?
A. Citric acid
B. Fumaric acid
C. Gibberellic acid
D. Lactic acid
Answer: B
Clarification: Rhizopus nigricans is used for the production of fumaric acid which is used in the manufacture of alkyd resins and wetting agents.

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Microbiology Problems focuses on “Viruses Containing Double – Stranded DNA”.

1. What is the shape of the nucleoid of poxviruses?
A. circular
B. brick-shaped
C. irregular
D. dumbbell-shaped
Answer: D
Clarification: Poxviruses contain double-stranded DNA, protein, and lipid and have a dumbbell-shaped nucleoid surrounded by two membrane layers.

2. The fatality rate for variola minor is ____________
A. 10-30%
B. 1-5%
C. 0.1-0.3%
D. 60-80%
Answer: C
Clarification: The less virulent variola minor (alastrim) has a fatality rate of only 0.1 to 0.3 percent which is very less in comparison to that of variola major.

3. For diagnosis of Smallpox viruses demonstration of Negri bodies is carried out.
A. True
B. False
Answer: B
Clarification: For diagnosis of Smallpox viruses the use of light microscopy to demonstrate inclusion bodies i.e., Guarnieri bodies in stained cells is carried out.

4. Which strain of adenoviruses can cause cancer?
A. Subgroup I
B. Subgroup II
C. Subgroup III
D. Subgroup IV
Answer: D
Clarification: Adenoviruses particularly those of subgroup IV can cause cancer or are oncogenic when inoculated into immunodeficient animals (newborn hamsters).

5. MDV virus affects which of the following?
A. chickens
B. cattle
C. humans
D. birds
Answer: A
Clarification: One of the animal herpesviruses is Marek’s disease virus (MDV), which affects the epithelium of feather follicles in chickens.

6. HSV-1 has been recognized as the causative agent of disease involving the genital tract.
A. True
B. False
Answer: B
Clarification: HSV-2 has been recognized as the causative agent of primary and recurrent disease involving the genital tract.

7. Which drug is used for healing genital herpes?
A. acyclovir
B. penicillin
C. erythromycin
D. tetracycline
Answer: A
Clarification: Topical application of the drug acyclovir can shorten the healing time in primary genital herpes but has little effect in the treatment of the recurrent form.

8. Mononucleosis is caused by which of the following viruses?
A. VZV
B. HSV
C. EBV
D. HIV
Answer: C
Clarification: Epstein-Barr Virus (EBV) is the causative agent of infectious mononucleosis, a self-limiting disease that occurs in up to 80 percent of the population.

9. What is the size of papillomaviruses?
A. 30 nm
B. 45 nm
C. 2 nm
D. 55 nm
Answer: D
Clarification: The Papovaviruses are divided into two major groups among which one is papillomaviruses which are 55 nm in diameter.

10. SV 40 causes diseases in which animals?
A. monkeys
B. rabbits
C. humans
D. cattle
Answer: A
Clarification: SV 40 occurs in monkeys and it was first discovered as a latent virus in cultures of rhesus monkey kidney cells.

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