Clinical microbiology: automated blood 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: automated blood culture

Sample item

An automated blood culture system flags a bottle as positive after 14 hours of incubation. Which principle underlies the detection, and what is the immediate next laboratory step?

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

The answer and the reasoning

A. Continuous sensor monitoring of carbon dioxide released by growing organisms, followed by Gram stain and subculture

Systems such as BACTEC and BacT/ALERT monitor the bottle continuously with a sensor that responds to carbon dioxide produced by microbial metabolism. A positive signal prompts an urgent Gram stain, which is reported to the clinician, together with subculture and rapid identification and susceptibility testing. Continuous monitoring detects growth earlier than visual inspection.

Option by option

  • A. Continuous sensor monitoring of carbon dioxide released by growing organisms, followed by Gram stain and subculture (correct)

    Correct. CO2 sensing flags growth, and Gram stain with subculture guides early therapy.

  • B. Detection of bacterial DNA by PCR, followed by discarding the bottle

    These systems detect growth, not DNA, and a positive bottle is never discarded.

  • C. Measurement of oxygen consumption only, followed by antibiotic susceptibility without Gram stain

    Detection relies on CO2 sensors, and a Gram stain is performed before susceptibility testing.

  • D. Turbidity measured by the naked eye each morning, followed by waiting 48 hours

    Visual turbidity checks are slower and are not how automated systems work.

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, Continuous sensor monitoring of carbon dioxide released by growing organisms, followed by Gram stain and subculture. Systems such as BACTEC and BacT/ALERT monitor the bottle continuously with a sensor that responds to carbon dioxide produced by microbial metabolism.

Why is "Detection of bacterial DNA by PCR, followed by discarding the bottle" not the answer?

These systems detect growth, not DNA, and a positive bottle is never discarded.

Why is "Measurement of oxygen consumption only, followed by antibiotic suscep…" not the answer?

Detection relies on CO2 sensors, and a Gram stain is performed before susceptibility testing.

Why is "Turbidity measured by the naked eye each morning, followed by waiting…" not the answer?

Visual turbidity checks are slower and are not how automated systems work.

What concept does this question test?

It tests Clinical microbiology: automated blood culture in Microbiology. A positive signal prompts an urgent Gram stain, which is reported to the clinician, together with subculture and rapid identification and susceptibility testing. Continuous monitoring detects growth earlier than visual inspection.

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 Clinical microbiology: automated blood 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.