Characterization of Glycopeptide-resistant Enterococci from U.S. Hospitals

We examined 105 clinical isolates of glycopeptide-resistant enterococci collected from 31 U.S. hospitals in 14 states during May 1988 to July 1992. The isolates included 82 Enterococcus faecium, 8 E. faecalis, 6 Enterococcus spp., 5 E. gallinarum, 3 E. casseliflavus, and 1 E. raffinosus. The isolates were categorized into the following four phenotypes of glycopeptide resistance on the basis of their MIC patterns: (i) 70 VanA (vancomycin [Vm] MIC, > or = 64 micrograms/ml; teicoplanin [Tei] MIC, 16 to > or = 128 micrograms/ml), (ii) 26 VanB (Vm MIC, 16 to 1,024 micrograms/ml; Tei MIC, < or = 2 micrograms/ml), (iii) 5 VanC (Vm MIC, 4 to 16 micrograms/ml; Tei MIC, < or = 2 micrograms/ml) in E. gallinarum, and (iv) 3 E. casseliflavus and 1 E. raffinosus isolates for which Vm MICs were 4 to 16 micrograms/ml and Tei MICs were < or = 1 micrograms/ml were called unclassified. Of the 101 isolates with the VanA, VanB, and VanC phenotypes, 99 were confirmed by production of a specific 1,030-, 433-, or 796-bp polymerase chain reaction product, respectively, and hybridization with the respective gene probe. The vanA gene was also detected in the E. raffinosus isolate for which the Vm MIC was 16 micrograms/ml and the Tei MIC was 1 microgram/ml. The vanA gene was located on either a 34- or a 60-kb plasmid in all of the U.S. isolates examined. Pulsed-field gel electrophoresis demonstrated both intrahospital and interhospital diversity among Vmr enterococci in the United States and was more useful than plasmid analysis for epidemiologic studies.