Emerging multiply resistant enterococci among clinical isolates. I. Prevalence data from 97 medical center surveillance study in the United States. Enterococcus Study Group.

To assess the evolving problem of therapeutic drug resistances among enterococci, we organized a comprehensive national (United States) surveillance trial using 99 recruited microbiology laboratories in 48 of the 49 contiguous states or districts. All but two sites completed the protocol that generated information from nearly 2000 enterococci, usually isolated from blood cultures. All strains were speciated by the same method (API 20S) and were susceptibility tested by three methods (broth microdilution, disk diffusion, and Etest) against ampicillin, penicillin, vancomycin, teicoplanin, gentamicin, and streptomycin. Strains resistant to a glycopeptide or penicillin, or possessing high-level aminoglycoside resistance were referred to the monitor's laboratory for validation and additional susceptibility testing against other alternative antimicrobial agents. The most common species were Enterococcus faecalis and Enterococcus faecium. However, antimicrobial resistance occurred most often among the E. faecium isolates. Twenty-three percent of participant centers (22 sites) reported 87 vancomycin-resistant isolates, which accounts for 4.4% of the isolates evaluated. A recent audit (March 1994) of the laboratories not reporting vancomycin resistance during the study interval (October-December 1992) revealed that 61% of sites have now recognized these strains, a threefold increase in 12-15 months. Teicoplanin remained active against 28% (Van B phenotype) of vancomycin-resistant enterococci (10 E. faecalis, 13 E. faecium, and one Enterococcus spp.). Ampicillin-resistant beta-lactamase-positive strains were found only at one medical center (two strains, 0.2% of referred or validated strains); however, ampicillin-resistant strains represented 12% of all enterococcal, but nearly 60% of E. faecium strains.(ABSTRACT TRUNCATED AT 250 WORDS)