Disinfection: phenol coefficient tests: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

Try it

Microbiology · Disinfection: phenol coefficient tests

Sample item

A hospital wants to compare a new disinfectant with phenol under conditions that mimic soiled surfaces, with organic matter added to the test. Which test is designed for this?

AIn-use (Maurer) testBRideal-Walker testCChick-Martin testDKirby-Bauer test

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Chick-Martin test

The Rideal-Walker test gives a phenol coefficient using clean suspensions of Salmonella Typhi. The Chick-Martin modification adds organic matter (dried yeast or faeces) to represent real soiling, which lowers the activity of many disinfectants. The result is a ratio of the disinfectant dilution to the phenol dilution that gives the same kill.

Option by option

A. In-use (Maurer) test
The in-use test checks whether a disinfectant in routine use is contaminated, not its coefficient against phenol.
B. Rideal-Walker test
The Rideal-Walker test is performed without organic matter and tends to overestimate efficacy.
C. Chick-Martin test (correct)
Correct. The Chick-Martin test includes organic matter in the assay.
D. Kirby-Bauer test
Kirby-Bauer is an antibiotic disk-diffusion susceptibility test, not a disinfectant test.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is C, Chick-Martin test. The Rideal-Walker test gives a phenol coefficient using clean suspensions of Salmonella Typhi.

Why is "In-use (Maurer) test" not the answer?

The in-use test checks whether a disinfectant in routine use is contaminated, not its coefficient against phenol.

Why is "Rideal-Walker test" not the answer?

The Rideal-Walker test is performed without organic matter and tends to overestimate efficacy.

Why is "Kirby-Bauer test" not the answer?

Kirby-Bauer is an antibiotic disk-diffusion susceptibility test, not a disinfectant test.

What concept does this question test?

It tests Disinfection: phenol coefficient tests in Microbiology. The Chick-Martin modification adds organic matter (dried yeast or faeces) to represent real soiling, which lowers the activity of many disinfectants. The result is a ratio of the disinfectant dilution to the phenol dilution that gives the same kill.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Disinfection: phenol coefficient tests?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.