Enterococci may be resistant to penicillins via two distinct mechanisms. The first is β-lactamase production (mediating resistance to penicillin and ampicillin), which has been reported for E. faecalis isolates from several locations in the United States and other countries. Because the amount of β-lactamase produced may be insufficient for detection by routine antibiotic susceptibility testing, isolates from serious infections should be screened specifically for βlactamase production with a chromogenic cephalosporin or another method. For the treatment of β-lactamase–producing strains, vancomycin, ampicillin/sulbactam, amoxicillin/clavulanate, imipenem, or meropenem may be used in combination with gentamicin. .
