Correct Answer: A

Rationale: Metronidazole exerts its antimicrobial activity by entering susceptible bacterial and protozoal cells where it is reduced to reactive metabolites that interact with DNA, causing strand breaks and inhibition of nucleic acid synthesis. This leads to rapid microbial death. The clinical improvement in diarrhea and fever indicates successful eradication of anaerobic or protozoal infection. Unlike cell wall inhibitors or antifolate agents, metronidazole’s unique redox mechanism makes it especially effective against anaerobes and protozoa such as Giardia and Entamoeba.

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