Outbreak of vancomycin-resistant enterococci in a hospital in Gdansk, Poland, due to horizontal transfer of different Tn1546-like transposon variantsand clonal spread of several strains

Twenty-two vancomycin-resistant enterococcal (VRE) isolates of the VanA phe notype (21 Enterococcus faecium isolates and 1 E. faecalis isolate), repres entative of a large outbreak that occurred in a hospital in Gdansk, Poland, were studied. All of the isolates demonstrated resistance to a wide variet y of other antimicrobial agents in addition to glycopeptides. Several lines of evidence suggested that the outbreak most probably consisted of two epi demics that followed the independent introduction of VanA determinants into two separate hematological wards of the hospital. This hypothesis is suppo rted by the fact that isolates recovered in these wards possessed two diffe rent polymorphs of the highly conserved DNA region encompassing the vanRSHA X genes and two distinct polymorph types of Tn1546-like transposons, which contain these genes, According to pulsed-field gel electrophoresis data, th e outbreak in the adult hematology ward (HW) was highly polyclonal, which s uggested a major role for the horizontal transmission of Tn1546-like elemen ts among nonrelated strains of E, faecium and E, faecalis in this environme nt. On the other hand, the outbreak in the pediatric hematology ward (PHW) was most probably due to the clonal spread of two epidemic E. faecium strai ns, which had exchanged a plasmid carrying the Tn1546-like transposon, Rest riction fragment length polymorphism studies of transposons and their inser tion loci in plasmid DNA have suggested that numerous isolates from both HW and PHW contained two or more copies of Tn1546-like elements that underwen t diversification due to various genetic modifications, The reported data d emonstrated a very complex epidemiology of the first, and up to now the onl y, VanA VRE outbreak characterized in Poland.