Primary care evaluation is requested for a 52-year-old male reporting four weeks of profound fatigue, night sweats, and unintentional weight loss. The patient underwent an uncomplicated cystoscopy for benign prostatic hyperplasia two months ago. Vital signs include a temperature of 38.2°C (100.8°F), blood pressure of 118/76 mmHg, and a heart rate of 94/min. Physical examination reveals splinter hemorrhages on the bilateral fingernails and a new grade III/VI holosystolic murmur loudest at the cardiac apex. Transesophageal echocardiography demonstrates a 1.4-cm oscillating mass on the anterior leaflet of the mitral valve. Four out of four blood culture bottles grow *Enterococcus faecalis*. Antimicrobial susceptibility testing reveals the following:
| Antimicrobial | Interpretation |
|---|---|
| Ampicillin | Susceptible |
| Penicillin | Susceptible |
| Vancomycin | Susceptible |
| Gentamicin (High-Level) | Resistant |
| Streptomycin (High-Level) | Resistant |
Based on the antimicrobial susceptibility results, which of the following is the most appropriate definitive intravenous antibiotic regimen?
- Ampicillin and ceftriaxoneAnswer
- BAmpicillin and gentamicin
- CDaptomycin monotherapy
- DVancomycin and piperacillin-tazobactam
- EVancomycin and gentamicin
Answer
To achieve bactericidal activity in HLAR *E. faecalis*, a dual beta-lactam regimen of ampicillin and ceftriaxone is utilized. While enterococci are intrinsically resistant to cephalosporins due to low affinity for specific penicillin-binding proteins (PBPs, primarily PBP5), ampicillin effectively binds PBP4 and PBP5, while ceftriaxone binds PBP2 and PBP3. This complementary saturation of PBPs results in a powerful synergistic bactericidal effect. Notably, because of its equivalent efficacy and lack of nephrotoxicity, ampicillin plus ceftriaxone is now widely considered a first-line therapy for all *E. faecalis* endocarditis cases, even in the absence of HLAR.