Multiplicity of genetic backgrounds among vancomycin-resistant Enterococcus faecium isolates recovered from an outbreak in a New York City hospital.

A total of 182 vancomycin-resistant Enterococcus faecium and 6 Enterococcus faecalis inpatient isolates recovered during a 2-year period (1990-1992) in a New York City hospital were analyzed by molecular fingerprinting techniques, pulsed-field gel electrophoresis (PFGE), of chromosomal SmaI digests combined with Southern hybridization using vanA and vanB2-specific DNA probes. Of the 180 isolates hybridizing with these probes, 153 carried the vanA and 27 the vanB gene. As many as 21 different PFGE types and a total of 54 subtypes were identified among the isolates, and the size of vanA and vanB-hybridizing DNA fragments also showed a wide range of sizes, from about 37 to over 280 kb (in vanA) or 140 kb (in vanB), suggesting extensive recombination, including chromosomal integration, of the resistance genes in the isolates. Close to one-third, 46, of the 148 isolates from 1992 belonged to two closely related PFGE subtype variants, each of which carried a 48 kb vanA hybridizing DNA fragment. Spread of this clone appears to be mainly responsible for the substantial increase in the prevalence of vancomycin-resistant E. faecium in early 1992.