vanA and vanB incorporate into an endemic ampicillin-resistant vancomycin-sensitive Enterococcus faecium strain: Effect on interpretation of clonality

Clonal spread and horizontal transfer in the spread of vancomycin resistanc e genes were investigated. Multiplex PCR, pulsed-field gel electrophoresis (PFGE), hybridization of enterococcal plasmids with the vanA and vanB probe s, and sequencing of a fragment of vanB were used in the analysis, Before M ay 1996, 12 vancomycin-resistant Enterococcus faecium (VRE) isolates were f ound in Finland, Between May 1996 and October 1997, 156 VRE isolates were f ound in the Helsinki area. Between December 1997 and April 1998, fecal samp les from 359 patients were cultured for VRE, One new case of colonization w ith VRE was found. During the outbreak period, 88% (137 of 155) of the VRE isolates belonged to two strains (VRE types I and II), as determined by PFG E, Each VRE type I isolate possessed vanB, and five isolates also had vanA. Of the 34 VRE type II isolates, 27 possessed vanA and 7 possessed vanB, Fi fteen of 21 (71%) ampicillin-resistant, vancomycin-sensitive E, faecium (VS E) isolates found during and after the outbreak period in one ward were als o of type II. Two VSE type II isolates were found in the hospital before th e outbreak in 1995, By PFGE, the three groups (vanA, vanB, or no van gene) of type II shared the same hand differences with the main type of VRE type II with vanA, None of the differences was specific to or determinative for any of the groups, Our material suggests that vanA and vanB incorporate int o an endemic ampicillin-resistant VSE strain.