PCR fragment length polymorphism analysis of vancomycin-resistant Enterococcus faecium

In this study, the glycopeptide resistance element, Tn1546, in 124 VanA Ent erococcus faecium clinical isolates from 13 Michigan hospitals was evaluate d using PCR fragment length polymorphism. There were 26 pulsed-field gel el ectrophoresis (PFGE) types, which consisted of epidemiologically related an d unrelated isolates from separate patients (1992 to 1996). Previously publ ished oligonucleotides specific for regions in the vanA gene cluster of Tn1 546 were used to amplify vanRS, vanSH, vanHAX, vanXY, and vanYZ. The glycop eptide resistance element, Tn1546, of E. faecium 228 was used as the basis of comparison for all the isolates in this study. Five PCR fragment length patterns were found, as follows. (i) PCR amplicons were the same size as th ose of EF228 for all genes in the vanA cluster in 19.4% of isolates. (ii) T he PCR amplicon for vanSH was larger than that of EF228 (3.7 versus 2.3 kb) due to an insertion between the vanS and vanH genes (79.2% of isolates). ( iii) One isolate in a unique PFGE group had a vanSH amplicon larger than th at of EF228 (5.7 versus 2.3 kb) due to an insertion in the vanS gene and an insertion between the vanS and vanH genes. (iv) One isolate did not produc e a vanSH amplicon, but when vanS and vanH were amplified separately, both amplicons were the same size as those as EF228. (v) One isolate had a vanYZ PCR product larger than that of EF228 (2.8 versus 1.6 kb). This study show s that in a majority of the VanA E. faecium isolates, Tn1546 is altered com pared to that of EF228. A total of 79.2% of the study isolates had the same -size insertion between the vanS and vanH genes. The results of this study show dissemination of an altered Tn1546 in heterologous VanA E. faecium in Michigan hospitals.