Clinical microbiology: quantitative urine culture: 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.

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Microbiology · Clinical microbiology: quantitative urine culture

Sample item

A 26-year-old woman has dysuria. A 0.001 mL calibrated loop of her midstream urine is plated on CLED agar, and 150 colonies of Escherichia coli grow overnight. What is the bacterial count, and how is it interpreted?

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

The answer and the reasoning

A. 1.5 x 10^5 CFU/mL, significant bacteriuria

Count per mL equals colonies divided by volume plated: 150 divided by 0.001 mL gives 150,000, or 1.5 x 10^5 CFU/mL. Kass criteria define significant bacteriuria as 10^5 CFU/mL or more of a single organism in a clean-catch sample, although lower counts can be significant in symptomatic patients.

Option by option

  • A. 1.5 x 10^5 CFU/mL, significant bacteriuria (correct)

    Correct. 150 / 0.001 = 150,000 CFU/mL, above the 10^5 threshold.

  • B. 1.5 x 10^7 CFU/mL, heavy growth

    A count of 1.5 x 10^7 would need 15,000 colonies from a 0.001 mL loop, which cannot be counted on a plate.

  • C. 1.5 x 10^3 CFU/mL, borderline

    This arises from assuming a 0.1 mL inoculum, which is not what a 0.001 mL loop delivers.

  • D. 1.5 x 10^2 CFU/mL, contamination

    This forgets to correct for the 0.001 mL volume and reports the raw colony number.

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.

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Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is A, 1.5 x 10^5 CFU/mL, significant bacteriuria. Count per mL equals colonies divided by volume plated: 150 divided by 0.

Why is "1.5 x 10^7 CFU/mL, heavy growth" not the answer?

A count of 1.5 x 10^7 would need 15,000 colonies from a 0.001 mL loop, which cannot be counted on a plate.

Why is "1.5 x 10^3 CFU/mL, borderline" not the answer?

This arises from assuming a 0.1 mL inoculum, which is not what a 0.001 mL loop delivers.

Why is "1.5 x 10^2 CFU/mL, contamination" not the answer?

This forgets to correct for the 0.001 mL volume and reports the raw colony number.

What concept does this question test?

It tests Clinical microbiology: quantitative urine culture in Microbiology. 001 mL gives 150,000, or 1.5 x 10^5 CFU/mL. Kass criteria define significant bacteriuria as 10^5 CFU/mL or more of a single organism in a clean-catch sample, although lower counts can be significant in symptomatic patients.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Clinical microbiology: quantitative urine culture?

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.