Aminoglycoside antibiotics require oxygen-dependent active transport into bacteria. This explains why they are ineffective against:
- A Pseudomonas aeruginosa
- B Strictly anaerobic organisms such as Bacteroides fragilis ✓
- C Gram-positive aerobic bacteria such as Staphylococcus aureus
- D Mycobacterium tuberculosis
Correct answer: B. Strictly anaerobic organisms such as Bacteroides fragilis
Explanation
Aminoglycosides enter bacteria via electron transport chain-driven (EDP2) active uptake that requires an oxygen-dependent electrochemical gradient across the bacterial membrane. Strict anaerobes lack this oxidative uptake system, so aminoglycosides cannot penetrate their membranes in sufficient concentrations. This is why metronidazole (activated by anaerobic nitroreduction) is used for anaerobic infections, and why aminoglycosides are ineffective in abscess cavities, which are hypoxic.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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