Bacteriology: HACEK endocarditis: 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 · Bacteriology: HACEK endocarditis

Sample item

A 28-year-old with a bicuspid aortic valve and poor dentition has six weeks of low-grade fever and a new regurgitant murmur. Blood cultures show no growth at 2 days, but a slow-growing Gram-negative coccobacillus appears at day 7 on extended incubation. Which organism is most likely?

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

The answer and the reasoning

A. Aggregatibacter, a HACEK organism

HACEK organisms are fastidious oral-flora Gram-negative bacilli that cause subacute endocarditis, and they may need extended incubation of blood cultures. Coxiella and Bartonella usually fail to grow in routine blood culture at all.

Option by option

  • A. Aggregatibacter, a HACEK organism (correct)

    Correct. Slow-growing oral Gram-negative coccobacilli causing endocarditis are HACEK organisms.

  • B. Bartonella quintana

    Bartonella quintana is a fastidious organism that generally needs special media or serology.

  • C. Enterococcus faecalis

    Enterococcus faecalis grows within 24 hours as Gram-positive cocci.

  • D. Coxiella burnetii

    Coxiella burnetii is an obligate intracellular organism that does not grow on routine culture.

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, Aggregatibacter, a HACEK organism. HACEK organisms are fastidious oral-flora Gram-negative bacilli that cause subacute endocarditis, and they may need extended incubation of blood cultures.

Why is "Bartonella quintana" not the answer?

Bartonella quintana is a fastidious organism that generally needs special media or serology.

Why is "Enterococcus faecalis" not the answer?

Enterococcus faecalis grows within 24 hours as Gram-positive cocci.

Why is "Coxiella burnetii" not the answer?

Coxiella burnetii is an obligate intracellular organism that does not grow on routine culture.

What concept does this question test?

It tests Bacteriology: HACEK endocarditis in Microbiology. Coxiella and Bartonella usually fail to grow in routine blood culture at all.

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 Bacteriology: HACEK endocarditis?

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.