Aminoglycosides are highly active against aerobic Gram-negative bacilli such as E. coli, Klebsiella and Pseudomonas, yet they are essentially inactive against anaerobic bacteria and have poor activity against streptococci acting alone. The pharmacological explanation is:

• A Anaerobes and streptococci lack the 30S ribosomal subunit target
• B Anaerobes possess constitutively expressed aminoglycoside-modifying enzymes
• C Uptake of aminoglycosides into bacteria is an oxygen-dependent active transport process ✓
• D The low extracellular pH at anaerobic sites destroys the drugs chemically

Explanation

Aminoglycosides enter bacteria through an energy-dependent, oxygen-requiring active transport across the inner membrane, so organisms growing anaerobically take up little drug and are resistant. This also explains the classic synergy between aminoglycosides and cell-wall-active agents such as penicillins, which disrupt the wall and enhance drug entry. The ribosomal 30S target is present in all bacteria, and modifying enzymes are acquired, not constitutive.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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