Clonal dissemination and colony morphotype variation of vancomycin-resistant Enterococcus faecium isolates in metropolitan Detroit, Michigan.

Thirty-two isolates of vancomycin-resistant Enterococcus faecium (VRE) recovered from 25 patients hospitalized at six hospitals in the metropolitan Detroit, Mich., area over a 32-month period were examined for relatedness by repetitive-sequence PCR (rep-PCR). All isolates were shown to carry the vanA gene by PCR. The rep-PCR patterns generated from each isolate showed that the first three VRE isolates obtained from hospital A between June 1992 and February 1994 were distinct strains. Thereafter, all VRE isolates originating from hospital A and those collected from five other area hospitals had identical rep-PCR patterns. On detailed examination, subcultures of 25 of the 32 VRE isolates produced two distinct colony types characterized phenotypically by a rough and a smooth appearance, respectively. Both colony types retained the vanA locus and the rep-PCR pattern of the primary isolate. These data suggest that a single strain of VRE with the capacity to produce two colonial variants has been disseminated to several Detroit-area hospitals. The clinical significance of the colonial morphotypes is unclear.