Aminoglycosides such as gentamicin show excellent activity against aerobic Gram-negative bacilli but are consistently inactive against anaerobic organisms such as Bacteroides fragilis. The pharmacological basis of this anaerobic inactivity is:

• A Anaerobes lack the 30S ribosomal subunit target of aminoglycosides
• B Anaerobes possess efflux pumps that rapidly export aminoglycosides
• C Aminoglycoside entry into the bacterial cell is an oxygen-dependent, energy-requiring transport process ✓
• D The low intracellular pH of anaerobes inactivates aminoglycosides

Explanation

Aminoglycosides cross the bacterial envelope by passive diffusion followed by an active, oxygen-dependent transport system driven by the electron transport chain. Strict anaerobes lack oxidative metabolism, so uptake fails and the drug never reaches the ribosome. The 30S target is present in anaerobes, ruling out option A, and efflux or pH effects are not the accepted explanation. This is why aminoglycosides must be combined with an anti-anaerobic agent such as metronidazole or clindamycin for mixed intra-abdominal infections.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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