Aminoglycosides are highly active against aerobic Gram-negative bacilli but have NO clinically useful activity against anaerobic bacteria. The basis for this selective spectrum is:

• A The oxygen-dependent electron transport chain-mediated active uptake system is absent in anaerobes ✓
• B Aminoglycosides are rapidly hydrolysed by anaerobic bacterial beta-lactamases
• C Aminoglycosides are actively effluxed by anaerobes via TolC-like channels
• D Aminoglycosides cannot cross the outer membrane of anaerobes due to lipopolysaccharide differences

Explanation

Aminoglycoside uptake across the bacterial inner membrane is an energy-requiring process that depends on the electron transport chain and thus on molecular oxygen. Anaerobes lack this oxidative metabolism, so the drug cannot enter the cell in sufficient concentration to reach its ribosomal target. This is the textbook explanation for their obligate aerobe spectrum. Option B is wrong because aminoglycosides are not beta-lactams.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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