High-level aminoglycoside resistance in Enterococcus faecalis is clinically significant because it eliminates which therapeutic advantage of aminoglycoside combination therapy?

• A The ability to use aminoglycosides as monotherapy for enterococcal infections
• B The post-antibiotic effect of aminoglycosides against enterococci
• C The synergistic bactericidal effect achieved when aminoglycosides are combined with cell wall-active agents (penicillin/vancomycin) ✓
• D The ability of aminoglycosides to penetrate the enterococcal biofilm

Explanation

Enterococci are inherently tolerant to aminoglycosides (high MIC) because of reduced drug uptake in the absence of cell wall synthesis inhibition. When a cell wall-active agent (penicillin or vancomycin) is combined with an aminoglycoside, the disrupted cell wall allows aminoglycoside entry, producing a synergistic bactericidal effect essential for treating serious enterococcal infections like endocarditis. High-level aminoglycoside resistance (HLAR) — mediated by aminoglycoside-modifying enzymes (AMEs) — abolishes this synergy even with combination therapy, leaving clinicians without a reliable bactericidal regimen.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.