Successful treatment of persistent bacteremia due to vancomycin-resistant, ampicillin-resistant Enterococcus faecium

Emergence of vancomycin-resistant enterococci has become an increasing problem in many medical centers. We report a liver transplant recipient with vancomycin-resistant Enterococcus faecium bacteremia who was successfully treated using very high dose continuous infusion ampicillin/sulbactam, plus gentamicin after he remained bacteremic on high dose ampicillin and gentamicin. At our institution, 83% of E. faecium isolates from 1994 were inhibited by ampicillin/sulbactam compared to 66% for ampicillin at an MIC less than or equal to 64 mu g/ml. None of these strains produced beta-lactamase, suggesting sulbactam may have an unexplained beneficial effect against some enterococci. Although an MIC of less than or equal to 8 mu g/ml is required for ampicillin to be considered active against enterococci, much higher levels of ampicillin or ampicillin/sulbactam are safely achievable, The response of our patient and the reported in vivo data have implications for future treatment of this pathogen, and may necessitate a reevaluation of susceptibility interpretation guidelines by clinical laboratories, and therapeutic drug dosing by clinicians.