Infection control: biofilm on prosthetic devices: 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 · Infection control: biofilm on prosthetic devices

Sample item

A patient with a prosthetic knee has persistent infection with Staphylococcus epidermidis despite antibiotics showing susceptibility in vitro. Cure requires removal or exchange of the prosthesis. Which property of the organism best explains this?

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

The answer and the reasoning

D. Biofilm formation with polysaccharide intercellular adhesin that shields bacteria on the implant

Staphylococcus epidermidis colonises foreign material and forms a biofilm of extracellular polysaccharide slime, with adhesins encoded by the ica operon. Bacteria inside the biofilm grow slowly and are protected from host defences and antibiotics, so susceptibility testing of planktonic cells does not predict cure. Removal of the device is often needed.

Option by option

  • A. Intracellular survival inside neutrophils only

    Intracellular neutrophil survival does not explain device-associated persistence.

  • B. Spore formation on the implant surface

    Staphylococci do not form spores.

  • C. Production of a potent exotoxin that destroys bone

    S. epidermidis is not known for a bone-destroying exotoxin.

  • D. Biofilm formation with polysaccharide intercellular adhesin that shields bacteria on the implant (correct)

    Biofilm with adhesin-mediated slime shields organisms from drugs and immune cells.

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 D, Biofilm formation with polysaccharide intercellular adhesin that shields bacteria on the implant. Staphylococcus epidermidis colonises foreign material and forms a biofilm of extracellular polysaccharide slime, with adhesins encoded by the ica operon.

Why is "Intracellular survival inside neutrophils only" not the answer?

Intracellular neutrophil survival does not explain device-associated persistence.

Why is "Spore formation on the implant surface" not the answer?

Staphylococci do not form spores.

Why is "Production of a potent exotoxin that destroys bone" not the answer?

S. epidermidis is not known for a bone-destroying exotoxin.

What concept does this question test?

It tests Infection control: biofilm on prosthetic devices in Microbiology. Bacteria inside the biofilm grow slowly and are protected from host defences and antibiotics, so susceptibility testing of planktonic cells does not predict cure. Removal of the device is often needed.

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 Infection control: biofilm on prosthetic devices?

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.