Bacterial growth: phases of the growth curve: 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 · Bacterial growth: phases of the growth curve

Sample item

A culture of Escherichia coli is exposed to a beta-lactam antibiotic during different phases of growth. In which phase are the bacteria most susceptible?

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

The answer and the reasoning

B. Logarithmic (exponential) phase

Beta-lactams inhibit cell wall synthesis, so they kill only cells that are actively dividing and making peptidoglycan. In the logarithmic phase cells divide at a constant maximal rate and are uniform in size and metabolism. In the stationary phase, growth and death balance, and secondary metabolites and spores are produced.

Option by option

  • A. Decline (death) phase

    In the decline phase most cells are dying and few are actively synthesising cell wall.

  • B. Logarithmic (exponential) phase (correct)

    Correct. Rapidly synthesising cell walls are the target of beta-lactams.

  • C. Lag phase

    During lag the cells adapt and synthesise enzymes without dividing, so they are less affected.

  • D. Stationary phase

    Slowed or stopped division in the stationary phase reduces killing by cell wall inhibitors.

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 B, Logarithmic (exponential) phase. Beta-lactams inhibit cell wall synthesis, so they kill only cells that are actively dividing and making peptidoglycan.

Why is "Decline (death) phase" not the answer?

In the decline phase most cells are dying and few are actively synthesising cell wall.

Why is "Lag phase" not the answer?

During lag the cells adapt and synthesise enzymes without dividing, so they are less affected.

Why is "Stationary phase" not the answer?

Slowed or stopped division in the stationary phase reduces killing by cell wall inhibitors.

What concept does this question test?

It tests Bacterial growth: phases of the growth curve in Microbiology. In the logarithmic phase cells divide at a constant maximal rate and are uniform in size and metabolism. In the stationary phase, growth and death balance, and secondary metabolites and spores are produced.

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 Bacterial growth: phases of the growth curve?

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.