Antimicrobial Susceptibility Patterns of Common and Unusual Species of Enterococci Causing Infections in the United States

We collected 705 isolates of enterococci (1 per patient) from cultures of a variety of anatomic sites from patients at eight tertiary-care hospitals in six geographic regions of the United States. A total of 632 (90%o) Enterococcusfaecalis, 58 (8%) E. faecium, 5 E. gaUinarum, 4 E. avium, 3 E. casseliflavus, 1 E. raffinosus, and 1 E. hitae isolate and 1 biochemical variant of E. faecalis were identified; 606 (86%) of these isolates were associated with clinical infections. The most common sites of isolation were the urinary tract (402 [57%]), nonsurgical wounds (94 [13%]), the bloodstream (74 [10%o]), and surgical wounds (62 [9%o]). High-level resistance to gentamicin or streptomycin or both was detected in 265 (38%) of the isolates. We identified two E.faecalis isolates resistant to vancomycin (MICs, 32 and 128 ,g/ml) and 11 3-lactamase-producingE.faecalis isolates. E. faecium isolates were significantly more resistant than E. faecalis isolates to penicillin, ampicillin, piperacillin, imipenem, and ciprofloxacin (P < 0.001). The MICs for the 15 non-E. faecalis, non-E. faecium enterococci indicated variable resistance to ciprofloxacin and the penicillins. Antimicrobial susceptibility patterns vary among species of enterococci, and these organisms, while commonly resistant to high-level aminoglycosides, can also acquire resistance to vancomycin or the ability to produce 13-lactamase. Because of these diverse antimicrobial resistance mechanisms, successful treatment and control of enterococcal infections with current antimicrobial agents are becoming increasingly difficult.