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Microbiology (GATE)

Description: Proteins
Number of Questions: 15
Created by:
Tags: Proteins Enrichment Culture Techniques for Isolation of Microorganisms Methods in Microbiology
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Adding vancomycin to a stool sample helps in the selective isolation of

  1. Enterococci

  2. E. coli

  3. Campylobacter

  4. Klebsiella


Correct Option: C
Explanation:

Campylobacter is inherently resistant to vancomycin and is selectively isolated on addition of vancomycin.

Which of the following bacteria grows best in a broth medium with pH 5.35?

  1. Vibrio

  2. Lactobacillus

  3. Acetobacter aceti

  4. Natronomonas


Correct Option: B
Explanation:

Lactobacillus grows luxuriantly in broth having pH 5.35. This pH is optimum for the growth of Lactobacillus.

Thayer-Martin agar is used for isolation of genus Neisseria. Which of the following antibiotics is absent from Thayer-Martin agar?

  1. Vancomycin

  2. Colistin

  3. Nystatin

  4. Penicillin


Correct Option: D
Explanation:

Thayer-Martin medium does not contain penicillin as Neisseria is susceptible to it.

Which of the following organisms grows luxuriantly and creates a clear zone in Pikovskaya medium?

  1. Bacillus subtilis

  2. Pantoea agglomerans

  3. Streptomyces griseus

  4. Nocardia spp.


Correct Option: B
Explanation:

Pantoea agglomerans grows luxuriantly in Pikovskaya medium and creates a clear zone indicating phosphate solubilisation.

Hektoen enteric agar is a selective and differential agar. Green colonies on Hektoen enteric agar are indicative of which of the following?

  1. Salmonella

  2. Shigella

  3. Klebsiella

  4. Escherichia


Correct Option: B
Explanation:

Shigella produces green colonies on Hektoen enteric agar because it does not produce H2S from thiosulphate or ferric ammonium citrate in the medium.

Which of the following organisms exhibits selective growth and grape juice-like aroma on cetrimide agar?

  1. Staphylococcus aureus

  2. Escherichia coli

  3. Pseudomonas aeruginosa

  4. Proteus mirabilis


Correct Option: C
Explanation:

Pseudomonas selectively grows on cetrimide agar. Cetyltrimethylammonium bromide, a quaternary ammonium and cationic detergent, is the component of cetrimide agar and allows for the selective isolation of Pseudomonas aeruginosa. Cetyltrimethylammonium bromide, when in contact with bacteria, causes the release of nitrogen and phosphorus from the bacterial cell. Organisms other than P. aeruginosa are unable to withstand this germicidal activity. Pseudomonas aeruginosa produces a characteristic fruity or grape juice-like aroma due to the production of an aromatic compound called aminoacetophenone.

Which of the following statements is false regarding differential media?

  1. Differential media always use indicators for differentiating two organisms.

  2. Differential media exploit biochemical characteristics of a microorganism.

  3. Granada medium is differential for Staphylococcus aureus.

  4. Differential media are used for the detection of microorganisms and by molecular biologists to detect recombinant strains of bacteria.


Correct Option: C
Explanation:

This is false. Granada medium is differential for Streptococcus agalactiae. They grow as distinctive red colonies in this medium.

If TSI (triple sugar iron) slant is inoculated with a bacterial culture, a yellow slant and a pink butt are indicated. It indicates the presence of which of the following?

  1. Glucose fermentor

  2. Glucose and sucrose fermentor

  3. Glucose and lactose fermentor

  4. Sucrose and lactose fermentor


Correct Option: A
Explanation:

Yellow slant and pink butt (acid slant and alkaline butt) indicate that only glucose is fermented. So, only a glucose fermentor is in the bacterial culture.

Roll tube technique is used to obtain pure cultures of which of the following?

  1. Stringent anaerobes

  2. Facultative anaerobes

  3. Mycobacterium tuberculosis

  4. Mycoplasma


Correct Option: A
Explanation:

Roll tube technique is used for stringent anaerobes. It provides an ideal condition for the cultivation of stringent anaerobes (redox potential below - 300 mV) which can be only achieved by the supplementation of media with reducing agents. This method consists of a roller tube in which the organism to be cultivated is immobilised on the side of the tube by a film of serum or other media.

Which of the following processes employs DMSO?

  1. Lyophilisation

  2. Cryopreservation

  3. Micromanipulation

  4. Mineral oil preservation


Correct Option: B
Explanation:

In cryopreservation, DMSO is used as a cryoprotectant at 10% concentration.

Venkataraman Ramakrishna (VR) medium is a transport medium. It is used for the transportation of which of the following?

  1. Gonococci

  2. Strict anaerobes

  3. Vibrio cholerae

  4. Clostridium tetani


Correct Option: C
Explanation:

Venkataraman Ramakrishna (VR) medium is a transport medium for the transportation of feces from suspected cholera patients.  These samples contain vibrio cholerae.

A mixed culture containing caulobacter, campylobacter, citrobacter and corynaebacterium is inoculated in peptone broth containing 0.01% peptone and incubated aerobically. Which of the following bacteria will produce first turbidity in the medium?

  1. Citrobacter

  2. Caulobacter

  3. Campylobacter

  4. Corynaebacterium


Correct Option: B
Explanation:

Caulobacter naturally lives in dilute aquatic environment. It can grow in the medium with very low levels of carbon and nitrogen. In such minimal media, other bacteria fail to grow and caulobacter grows and produces turbidity.

Which of the following ingredients in MSA makes it selective for the genus Staphylococcus?

  1. Mannitol

  2. Peptone

  3. Sodium chloride

  4. Phenol red


Correct Option: C
Explanation:

MSA has a high concentration of sodium chloride that selects for members of the genus Staphylococcus as they can tolerate high saline levels. Organisms from other genera may grow, but very weakly.

Which of the following enrichment conditions would be ideal for Yersinia enterocolitica?

  1. Selenite-containing broth

  2. Alkaline nutrient broth with pH 8.0

  3. Alkaline bile oxalate-sorbosebroth with pH 7.6

  4. Taurocholate tellurite peptone water


Correct Option: C
Explanation:

Alkaline bile oxalate-sorbosebroth with pH 7.6 is the ideal condition for the enrichment of Yersinia enterocolitica.

Dubos broth base is used for the cultivation of Mycobacteria. Which of the following ingredients increases the growth by dispersing bacilli?

  1. Casein enzymatic hydrolysate

  2. Polysorbate 80

  3. Bovine albumin

  4. Calcium chloride


Correct Option: B
Explanation:

Polysorbate 80 increases the growth by dispersing bacilli. It also acts as a surfactant and supplies the essential fatty acids for replication.

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