The GATE Grind

GATE 2021 ES – Question 49

Environmental Microbiology · Microbiology and Health · 2 marks · Multiple select

For conventional water-quality MPN testing, select correct statements.

  1. Estimated indicator organisms are Gram-negative
  2. Based on a Poisson-distribution assumption
  3. Measures the exact microorganism count
  4. Includes pathogenic-virus quantification

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Show answer and explanation

Correct answer: (A) Estimated indicator organisms are Gram-negative; (B) Based on a Poisson-distribution assumption

Explanation

The conventional coliform MPN assay estimates Gram-negative indicator organisms using patterns of positive tubes. Random independent organism allocation is modelled by a Poisson distribution. Thus **A, B**. It is a statistical estimate, not an exact count, and this coliform test does not quantify viruses.

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