Question:
Anaerobes are intrinsically resistant to which class of antibiotics?
Anaerobes are intrinsically resistant to which class of antibiotics?
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Which antibiotic needs oxygen-dependent uptake that anaerobes cannot provide?
Updated On: Jun 24, 2026
- Beta lactam antibiotics
- Aminoglycosides
- Azithromycin
- Metronidazole
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The Correct Option is B
Solution and Explanation
Step 1: Recall how aminoglycosides enter bacteria. Their uptake across the membrane requires oxygen-dependent active transport.
Step 2: Apply to anaerobes. Anaerobic bacteria lack the oxidative metabolism needed to drive this uptake, so the drug cannot get in and they are intrinsically resistant.
Step 3: Define intrinsic resistance. It is the innate, inherent structural or functional ability of an organism to tolerate a drug class, reducing susceptibility from the outset.
Step 4: Exclude distractors. Metronidazole is in fact the drug of choice against anaerobes, and beta lactams and azithromycin have variable but not uniform intrinsic resistance. So option B is correct.
Step 2: Apply to anaerobes. Anaerobic bacteria lack the oxidative metabolism needed to drive this uptake, so the drug cannot get in and they are intrinsically resistant.
Step 3: Define intrinsic resistance. It is the innate, inherent structural or functional ability of an organism to tolerate a drug class, reducing susceptibility from the outset.
Step 4: Exclude distractors. Metronidazole is in fact the drug of choice against anaerobes, and beta lactams and azithromycin have variable but not uniform intrinsic resistance. So option B is correct.
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