Enterococcus faecalis is isolated from blood cultures of a patient with subacute infective endocarditis. Susceptibility testing shows resistance to ampicillin and high-level aminoglycoside resistance (HLAR). The isolate tests vancomycin-sensitive. What is the MOST appropriate antibiotic regimen?

• A Vancomycin alone
• B Ampicillin–sulbactam plus gentamicin
• C Vancomycin plus an aminoglycoside synergistically
• D Daptomycin or linezolid as monotherapy ✓

Explanation

Enterococcal endocarditis requires bactericidal synergistic therapy traditionally using a cell-wall active agent (penicillin/ampicillin/vancomycin) plus an aminoglycoside. However, with ampicillin resistance and high-level aminoglycoside resistance (HLAR — which abolishes synergy), both combinations are ineffective. For vancomycin-sensitive enterococci with HLAR and ampicillin resistance, alternatives such as daptomycin or linezolid (despite being bacteriostatic) are recommended by current guidelines. Vancomycin alone is insufficient for endocarditis, and synergy is lost with HLAR.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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