General microbiology: bacterial genetics: 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 · General microbiology: bacterial genetics

Sample item

In a patient's gut, a commensal Escherichia coli strain carrying a plasmid with several resistance genes transfers resistance to an incoming Shigella strain by direct cell-to-cell contact through a pilus. What is the best description of this event and its genetic element?

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

The answer and the reasoning

D. Conjugation of an R factor plasmid that carries a resistance transfer factor

Conjugation requires cell contact through a sex pilus and is the main route of spread of multidrug resistance among enteric Gram-negative bacilli. R factors are conjugative plasmids made of a resistance transfer factor (tra genes) and resistance determinants, often within transposons. Transduction, transformation and lysogenic conversion do not involve pilus-mediated contact.

Option by option

  • A. Transduction by a temperate bacteriophage

    Transduction needs a bacteriophage as vehicle, not direct contact.

  • B. Transformation by free DNA released from lysed bacteria

    Transformation is uptake of naked DNA and involves no pilus.

  • C. Lysogenic conversion by an integrated prophage

    Lysogenic conversion is acquisition of toxin or other genes from a prophage.

  • D. Conjugation of an R factor plasmid that carries a resistance transfer factor (correct)

    Correct. Plasmid-borne resistance moves by pilus-mediated conjugation.

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, Conjugation of an R factor plasmid that carries a resistance transfer factor. Conjugation requires cell contact through a sex pilus and is the main route of spread of multidrug resistance among enteric Gram-negative bacilli.

Why is "Transduction by a temperate bacteriophage" not the answer?

Transduction needs a bacteriophage as vehicle, not direct contact.

Why is "Transformation by free DNA released from lysed bacteria" not the answer?

Transformation is uptake of naked DNA and involves no pilus.

Why is "Lysogenic conversion by an integrated prophage" not the answer?

Lysogenic conversion is acquisition of toxin or other genes from a prophage.

What concept does this question test?

It tests General microbiology: bacterial genetics in Microbiology. R factors are conjugative plasmids made of a resistance transfer factor (tra genes) and resistance determinants, often within transposons. Transduction, transformation and lysogenic conversion do not involve pilus-mediated contact.

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 General microbiology: bacterial genetics?

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.