Category: MICROBIOLOGY Objective Questions

Microbiology Multiple Choice Questions on “Bacterial Recombination”.

1. The transfer of genes from one cell to another by a bacteriophage is known as __________________
A. Recombination
B. Conjugation
C. Transduction
D. Transformation
Answer: C
Clarification: In bacteria, genetic recombination results from three types of gene transfer among which transfer of genes from one cell to another by a bacteriophage is known as transduction.

2. Genetic recombination occurs between homologous chromosomes.
A. True
B. False
Answer: A
Clarification: Genetic recombination is the formation of a new genotype by reassortment of genes following an exchange of genetic material between two different chromosomes that have similar genes at corresponding sites. These are called homologous chromosomes and are from different individuals.

3. Bacterial recombination causes transformation of the recipient cell to _______________
A. donor cell
B. merozygote
C. zygote
D. recipient cell
Answer: B
Clarification: The recipient cell becomes a merozygote, a zygote that is a partial diploid and then recombination can take place.

4. Transfer of genes between cells that are in physical contact with one another is known as transformation.
A. True
B. False
Answer: B
Clarification: Transfer of genes between cells that are in physical contact with one another is known as conjugation.

5. Which of the enzymes are used to cut the recipient DNA?
A. endonuclease
B. exonuclease
C. ligases
D. polymerase
Answer: A
Clarification: Endonuclease acts on the recipient DNA causing nicks and excision of a fragment of DNA to be replaced by donor DNA.

6. The transfer of naked DNA from one cell to another is referred to as _______________
A. Transduction
B. Lysogeny
C. Transformation
D. Conjugation
Answer: C
Clarification: The transfer of cell-free or ‘naked’ DNA from one cell to another is called transformation.

7. The cell in which the F factor carries along with it some chromosomal genes are known as ____________
A. F⁺ cell
B. F^— cell
C. F’ cell
D. F’’’ cell
Answer: C
Clarification: Sometimes the F factor carries along with it some chromosomal genes and is termed as F’ factor, and the cell in which this has occurred is called an F’ cell.

8. What are bacteriocins?
A. proteins
B. toxins
C. plasmid
D. sex factor
Answer: A
Clarification: Bacteriocins are proteins that kill the same or closely related species of bacteria and are formed by bacteriocinogenic factors.

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Microbiology Multiple Choice Questions on “Diseases Caused by Protozoa”.

1. Animals that are routinely infected with a protozoan or parasite are termed as _______________
A. definitive host
B. intermediate host
C. reservoir host
D. parasitic host
Answer: C
Clarification: An animal (or human) that is routinely infected with a protozoan or parasite which can also infect humans is termed as a reservoir host.

2. For the malaria protozoa, mosquitoes are the definitive host.
A. True
B. False
Answer: A
Clarification: For the malaria protozoa, the mosquito is the definitive host, and humans or other vertebrates are the intermediate hosts.

3. Laboratory diagnosis of Entamoeba histolytica depends on identification in the ___________
A. blood
B. urine
C. saliva
D. stool
Answer: D
Clarification: Laboratory diagnosis of Entamoeba histolytica depends on identification in the stools. Search for the amoeba should be made as soon as possible after the stool is passed to be sure of the presence of living, motile forms.

4. African sleeping sickness is caused by which of the following protozoa?
A. Entamoeba histolytica
B. Trypanosoma gambiense
C. Leishmania donovani
D. Plasmodium vivax
Answer: B
Clarification: African sleeping sickness is caused by Trypanosoma gambiense and is transmitted by flying bite.

5. Most commonly Plasmodium ovale and Plasmodium malariae causes malaria in humans.
A. True
B. False
Answer: B
Clarification: Of the four species of Plasmodium protozoa that cause malaria in humans, P. falciparum and P. vivax are the two that most commonly cause infections.

6. After how many days of infection by mosquitoes do the symptoms for malaria occur?
A. 1-2
B. 3-5
C. 10-16
D. 20-30
Answer: C
Clarification: Symptoms usually occur 10 to 16 days after infection by the mosquitoes.

7. The schizonts enter which body part?
A. bloodstream
B. spleen
C. mouth
D. liver
Answer: D
Clarification: The sporozoites quickly enter the liver, where they divide and develop into multinucleated forms known as schizonts.

8. How much time does it take for the rupture of infected erythrocytes with P. vivax?
A. 24 h
B. 48 h
C. 72 h
D. 96 h
Answer: B
Clarification: The rupture of infected erythrocytes at the completion of schizogony occurs every 48 h with P. vivax and P. ovale.

9. The disease espundia is caused by which of the following protozoa?
A. Leishmania brasiliensis
B. Leishmania donovani
C. Leishmania tropica
D. Phlebotomus sp
Answer: A
Clarification: Leishmania brasiliensis causes the disease espundia which can then cause the infection for the disease leishmaniasis.

10. Leishmania organism are transmitted to humans by ______________
A. sandflies
B. tsetse flies
C. mosquitoes
D. bugs
Answer: A
Clarification: Leishmania organism are transmitted to humans by the bites of sandflies (genus Phlebotomus) harbored by dogs and other animals that serve as reservoirs for the parasites.

11. What is the incubation period for kala azar disease?
A. 24 h
B. 1 month
C. 2-4 months
D. 7 days
Answer: C
Clarification: Clinically, kala azar has a variable incubation period, usually 2 to 4 months. Onset may be gradual or sudden, and the source of the disease may be acute or chronic.

12. African sleeping sickness is caused by _______________
A. Trypanosoma cruzi
B. Trypanosoma gambiense
C. Trichomonas vaginalis
D. Leishmania tropica
Answer: B
Clarification: African sleeping sickness is caused by Trypanosoma gambiense and Trypanosoma rhodesiense.

13. Chagas’ disease is transmitted to humans by ________________
A. tsetse fly
B. mosquitoes
C. reduviid bugs
D. sandflies
Answer: C
Clarification: T.cruzi, the causative agent of Chagas’ disease is transmitted to humans by reduviid bugs (Triatoma, Rhodinas, and Panstrongylus), which are intermediate hosts as well as vectors for the parasites.

14. Where are the protozoa present during the acute stage of Chagas’ disease?
A. blood
B. spleen
C. liver
D. stool
Answer: A
Clarification: T. cruzi is present in the blood during the acute stage of Chagas’ disease. Fatality is due to a meningoencephalitis or myocardial failure.

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Microbiology Multiple Choice Questions on “Microbial Classification”.

1. Type strain is used for referring to?
A. species
B. genus
C. family
D. division
Answer: A
Clarification: Bacterial species consists of a special strain called type strain which have similar characteristics. Bacterial genus is composed of a collection of similar species and is referred to as type species.

2. The correct order of taxonomic groups from higher to lower rank is?
A. Kingdom—Order—Class—Family
B. Order—Class—Division—Family—Genus—Species
C. Kingdom—Order—Division—Family—Class—Genus—Species
D. Kingdom—Division—Class—Order—Family—Genus—Species
Answer: D
Clarification: Taxonomists have made the classification based on two qualities—stability and predictability. The order of taxonomic groups from higher rank to lower rank is: Kingdom—Division—Class—Order—Family—Genus—Species.

3. % Similarity (%S) of each strain to every other strain is calculated by which method?
A. Intuitive Method
B. Numerical Taxonomy
C. Genetic Relatedness
D. DNA homology experiments
Answer: B
Clarification: %S = NS
NS+ND
where, %S is % similarity of each strain to every other strain, NS is the number of characteristics that are the same for the two strains, and ND is the number of characteristics that are different. Thus this is determined by numerical taxonomy.

4. Two organisms which are very closely related to each other have which of the following property?
A. similar mol% G+C values
B. different mol% G+C values
C. similar mol% G+C values and heteroduplexes are formed
D. different mol% G+C values and heteroduplexes are not formed
Answer: C
Clarification: Two organisms of the same species that are very closely related to each other will have very similar mol% G+C values and their single strands of DNA molecules combine to form heteroduplexes. Organisms which are not closely related have different mol% G+C values and hence do not form heteroduplexes.

5. What are ribosomes composed of?
A. Proteins
B. DNA
C. RNA
D. Proteins and RNA
Answer: D
Clarification: Ribosomes, the small granular-appearing structures within the cell which manufacture proteins, are composed of proteins and RNA. The ribosomal RNA (rRNA. is coded for by only a small fraction of the DNA molecule, the rRNA cistrons.

6. If two organisms are distantly related and show no DNA homology there still may be similarity in their rRNA cistrons.
A. True
B. False
Answer: A
Clarification: The nucleotide sequence of rRNA genes has been found to be highly conserved. So even if two organisms are only distantly related and show no significant DNA homology, there still maybe similarity in the nucleotide sequences of their rRNA cistrons. The degree of similarity that exists can then be used as a measure of relatedness between organisms.

7. Which of the following are characteristics of archaebacterial different from eubacteria?
A. methane-producers
B. extreme halophiles
C. thermoacidophiles
D. methane-producers, extreme halophiles, and thermoacidophiles
Answer: D
Clarification: Eubacteria are the traditional, familiar ones that have received the most study. Archaebacteria the other group consists of methane producers, extreme halophiles and thermoacidophiles.

8. Which among the following come under Gram-positive eubacteria?
A. Clostridium
B. Actinomyces
C. Rhizobium
D. Clostridium, Actinomyces
Answer: D
Clarification: Based on rRNA oligonucleotide, Clostridium and Actinomyces come under Gram-positive eubacteria. Rhizobium belongs to Purple eubacteria.

9. Which among the following kingdoms were proposed by Whittaker?
A. Monera
B. Protista, Fungi
C. Plantae, Animalia
D. Monera,Protista,Fungi,Plantae,Animalia
Answer: D
Clarification: R.H.Whittaker classified microorganisms on the basis of nutritional requirements and formed Whittaker’s Five Kingdom and they are Monera (bacteria and cyanobacteria), Protista (microalgae and protozoa), Fungi (yeasts and molds), Plantae (multicellular green plants and higher algae) and Animalia (multicellular animals).

10. According to Bergey’s Manual of Systematic Bacteriology, prokaryotes that lack a cell wall belong to the group?
A. Gracilicutes
B. Firmicutes
C. Tenericutes
D. Mendosicutes
Answer: C
Clarification: Tenericutes are prokaryotes that lack a cell wall. Gracilicutes are prokaryotes with a complex cell-wall structure characteristic of Gram-negative bacteria. Firmicutes are prokaryotes with a cell wall structure characteristic of Gram-positive bacteria and Mendosicutes are prokaryotes that show evidence of an earlier phylogenetic origin.

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Microbiology Multiple Choice Questions on “Cultural Characteristics”.

1. The National Collection of Type Cultures is situated in ____________
A. France
B. England
C. Germany
D. Japan
Answer: B
Clarification: In England, the National Collection of Type Culture is in London which is a large central collection whose main purpose would be the acquisition, preservation, and distribution of authentic cultures of living organisms.

2. The American Type Culture Collection, located in Rockville, Maryland in the year 1980 has a collection of bacterial strain in what numbers?
A. 10,000
B. 11,000
C. 500
D. 11,500
Answer: D
Clarification: In the US the major collection is the American Type Culture Collection, located in Rockville, Maryland. In 1980 the collection included the following number of strains: bacteria-11,500; bacteriophages-300; algae-130; protozoa-720; fungi and fungal viruses-13700 etc.

3. Which of the following has a larger diameter?
A. well-separated colonies
B. crowded colonies
C. young colonies
D. old colonies
Answer: A
Clarification: Well-separated colonies have a larger diameter than those which are crowded together because widely separated colonies are subject to less competition for nutrients and less inhibition by toxic products of metabolism.

4. Surface texture of strains are related to virulence.
A. True
B. False
Answer: A
Clarification: For several species of pathogenic species, the surface texture of colonies may bear a relation to virulence. For example, Smooth colonies of S.pneumoniae or of Salmonella species are usually virulent, whereas Rough colonies are not.

5. What is the color of colonies of Staphylococcus aureus?
A. Pink
B. Red
C. Violet
D. Gold
Answer: D
Clarification: Staphylococcus aureus produces and retains water-insoluble pigments which give golden color to their colonies.

6. Pyoverdin is which type of pigment?
A. water-insoluble pigment
B. water-soluble pigment
C. fluorescent pigment
D. sparingly water-soluble pigment
Answer: C
Clarification: Pyoverdin is a fluorescent pigment and is water-soluble in which the agar medium around the colonies glows white or blue-green when exposed to ultraviolet light. It is produced by P.aeruginosa.

7. Growth in broth cultures occurs mainly in the form of__________
A. slightly turbid
B. heavy surface pellicle
C. sediment
D. viscous
Answer: B
Clarification: Growth in broth cultures occurs mainly in the form of a heavy surface pellicle and the medium below the pellicle is only slightly turbid.

8. Which bacteria among the following produces a water-insoluble pigment?
A. Mycobacterium kansasii
B. Pseudomonas aeruginosa
C. Chromobacterium violaceum
D. Pseudomonas chlororaphis
Answer: C
Clarification: Chromobacterium violaceum produces a water-insoluble pigment which causes its colonies to become violet in color.

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Microbiology Multiple Choice Questions on “World of Bacteria II – Gram – Positive Cocci”.

1. The cocci belonging to the family Dienococcaceae occur mainly in _______________
A. tetrads
B. diplococci
C. streptococci
D. staphylococci
Answer: A
Clarification: The cocci belonging to the family Deinococcaceae occurs mainly in tetrads or cubical packets.

2. The organisms belonging to the genus Deinococcus forms colonies of which color?
A. colourless
B. blue
C. red
D. violet
Answer: C
Clarification: The family Deinococcaceae contains a single genus Deinococcus which forms red colonies.

3. The family Micrococcaceae do not exhibit any unusual resistance to gamma and ultraviolet radiation.
A. True
B. False
Answer: A
Clarification: The family Micrococcaceae do not exhibit any unusual resistance to gamma and ultraviolet radiation. But the organisms belonging to family Deinococcaceae have an unusually high resistance to gamma and ultraviolet radiations.

4. Among the following which is positive for coagulase test?
A. Staphylococcus aureus
B. Staphylococcus epidermidis
C. Staphylococcus saprophyticus
D. E.coli
Answer: A
Clarification: Staphylococcus aureus is positive for coagulase test which is a test for the ability of the bacteria to cause blood plasma to clot.

5. Streptococcus are catalase-positive.
A. True
B. False
Answer: B
Clarification: Streptococcus are catalase-negative. The organisms are homofermentative i.e., the predominant end product of sugar fermentation is lactic acid.

6. Which of the following species of streptococci belongs to Lancefield group N?
A. S.pyogenes
B. S.mutans
C. S.pneumoniae
D. S.cremoris
Answer: D
Clarification: The streptococci are divided into categories known as the Lancefield groups based on differences in their cell-wall polysaccharides. S.cremoris belong to Lancefield group N and are harmless contaminants of milk and dairy products.

7. S.pneumoniae produces which of the following type of colonies?
A. alpha-haemolytic
B. beta-haemolytic
C. non-haemolytic
D. alpha-, beta-haemolytic
Answer: A
Clarification: S.pneumoniae are alpha-haemolytic i.e. colonies are surrounded by a cloudy, colorless or greenish zone of partially lysed erythrocytes.

8. Which of the following is the causative agent of dental caries?
A. S.pneumoniae
B. S.pyogenes
C. S.mutans
D. S.faecalis
Answer: C
Clarification: S.mutans inhabits the human oral cavity and is the major causative agent of dental caries.

9. Which of the following genus of species occurs in human feces?
A. Peptococcus
B. Coprococcus
C. Sarcina
D. Ruminococcus
Answer: B
Clarification: Coprococcus occurs in human feces and uses carbohydrates as a major source of carbon and energy.

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Microbiology Multiple Choice Questions on “Replication of Bacterial Viruses”.

1. Which of the following is the first step in replication by bacterial phages?
A. adsorption
B. penetration
C. transcription
D. assembly and release
Answer: A
Clarification: The first step in the infection of a host bacterial cell by a phage is adsorption. The infection of a host bacterial cell cannot occur without adsorption.

2. At what temperature incubation is required for the adsorption of phage T4 and DNA injection into E.coli?
A. 50 degree C
B. 15 degree C
C. 37 degree C
D. 80 degree C
Answer: C
Clarification: Phage T4 adsorption and DNA injection into E.coli spheroplasts require the phage particles to be incubated with spheroplasts at 37 degree C for 10 mins.

3. Which of the following is the correct sequence of events in replication by bacterial phage?
A. adsorption, pinning, DNA injection, sheath contraction
B. adsorption, pinning, sheath contraction, DNA injection
C. adsorption, absorption, sheath contraction, pinning
D. absorption, adsorption, DNA injection
Answer: B
Clarification: The first step in the process of replication by bacterial phage is adsorption to the host cell. This is followed by pinning when the tail pins attach to the cell surface. Then the sheath contracts driving the tail core into the cell through the cell membrane and then the virus injects its DNA into the cell.

4. The protein coat of the virus remains outside the host cell.
A. True
B. False
Answer: A
Clarification: The protein coat, which forms the phage head, and the tail structure of the virus remains outside the cell.

5. The delayed early genes codes for which of the following enzymes?
A. phage enzymes
B. RNA polymerase
C. nucleases
D. oxidases
Answer: A
Clarification: Delayed early genes code for phage enzymes which produce unique phage DNA constituents such as 5-hydroxymethylcytosines; which destroy precursors of cytosine deoxynucleotides so that no bacterial cytosine will be incorporated into phage DNA.

6. Which of the following enzymes transcribe late genes?
A. ligases
B. nucleases
C. RNA polymerase
D. restriction enzymes
Answer: C
Clarification: Delayed early genes code for second altered RNA polymerase that will transcribe the late genes.

7. In the growth curve of plaque-forming units, the time from infection until lysis is known as ____________________
A. eclipse period
B. rise period
C. burst period
D. latent period
Answer: D
Clarification: No newly released extracellular phages can be seen until lysis begins; the time from infection until lysis is the latent period.

8. What is the colour of the plaque formed?
A. yellow
B. opaque
C. clear
D. blue
Answer: C
Clarification: Growth of phage is indicated by the appearance of plaques that are clear zones, unlike the otherwise opaque growth of the host bacterium.

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