Enterococci. Biologic and epidemiologic characteristics and in vitro susceptibility.

Enterococci cause urinary tract infection (usually asymptomatic), 5% to 15% of cases of endocarditis, and rare cases of meningitis. Their role in polymicrobial infection in the abdomen and pelvis is difficult to assess. Ninety percent of enterococci are inhibited by 4 mg/L of penicillin G, by 2 mg/L of ampicillin, and by 6 mg/L of vancomycin. The penicillinase-resistant penicillins, cephalosporins, carbenicillin, and ticarcillin are at least fourfold less active against enterococci than penicillin G, whereas piperacillin has activity equivalent to penicillin G. The addition of an aminoglycoside to penicillin, ampicillin, vancomycin or piperacillin--which are not bactericidal against most strains of enterococci--results in more rapid and complete bacterial activity (ie, synergistic activity).