An Enterococcus faecalis isolate from a blood culture shows high-level resistance to gentamicin on screening with 500 μg/mL gentamicin agar. What is the clinical implication of this finding?

• A The combination of ampicillin and gentamicin will not demonstrate synergistic killing ✓
• B Gentamicin can still be used in combination with ampicillin for synergy
• C The isolate is resistant to all aminoglycosides including streptomycin
• D Vancomycin should be avoided in this patient

Explanation

High-level aminoglycoside resistance (HLAR) screening uses 500 μg/mL gentamicin or 120 μg/mL streptomycin. If resistant, the organism cannot achieve intracellular aminoglycoside concentrations high enough to synergize with cell wall active agents like ampicillin or vancomycin. The combination should not be used for synergy. Option C is wrong because gentamicin HLAR does not predict streptomycin HLAR, which is tested separately.

Reference: Mackie and McCartney Practical Medical Microbiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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