Clinical microbiology: ESBL treatment: 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: ESBL treatment

Sample item

A 70-year-old woman in a surgical ICU has Klebsiella pneumoniae bacteraemia. The isolate is resistant to ceftriaxone, ceftazidime and aztreonam, with zone enhancement towards the amoxicillin-clavulanate disc on double-disc synergy testing. Which class is the drug of choice for this serious infection?

ACeftriaxone at a higher doseBAztreonamCCefepimeDA carbapenem such as meropenem

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

The answer and the reasoning

D. A carbapenem such as meropenem

A pattern of third-generation cephalosporin and aztreonam resistance with clavulanate synergy indicates an extended-spectrum beta-lactamase, which hydrolyses penicillins, cephalosporins and aztreonam but not carbapenems and is inhibited by clavulanate. Carbapenems are the treatment of choice for serious ESBL infections, and their use makes carbapenemase surveillance important.

Option by option

A. Ceftriaxone at a higher dose
Increasing the dose cannot overcome enzymatic hydrolysis by the ESBL.
B. Aztreonam
Aztreonam is hydrolysed by ESBLs, as the resistance pattern already shows.
C. Cefepime
Cefepime may appear susceptible in vitro but is unreliable, because high inocula are hydrolysed.
D. A carbapenem such as meropenem (correct)
Correct. Carbapenems are stable to ESBL hydrolysis and are preferred for serious infection.

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 D, A carbapenem such as meropenem. A pattern of third-generation cephalosporin and aztreonam resistance with clavulanate synergy indicates an extended-spectrum beta-lactamase, which hydrolyses penicillins, cephalosporins and aztreonam but not carbapenems and is inhibited by clavulanate.

Why is "Ceftriaxone at a higher dose" not the answer?

Increasing the dose cannot overcome enzymatic hydrolysis by the ESBL.

Why is "Aztreonam" not the answer?

Aztreonam is hydrolysed by ESBLs, as the resistance pattern already shows.

Why is "Cefepime" not the answer?

Cefepime may appear susceptible in vitro but is unreliable, because high inocula are hydrolysed.

What concept does this question test?

It tests Clinical microbiology: ESBL treatment in Microbiology. Carbapenems are the treatment of choice for serious ESBL infections, and their use makes carbapenemase surveillance important.

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: ESBL treatment?

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.