Molecular analysis of diverse elements mediating VanA glycopeptide resistance in enterococci.

Differences were examined among 24 distinct elements mediating VanA-type glycopeptide resistance in enterococci isolated from hospital patients and non-human sources in the UK. The methods used included long-PCR restriction fragment length polymorphism (L-PCR RFLP) analysis and DNA hybridization. All elements had conserved vanRSHAX genes, but variation occurred upstream of vanR and downstream of vanX. Twenty-one VanA elements had significant alterations upstream of vanR in the transposition genes orf1 and orf2: either parts of these genes were absent or they were disrupted by IS1216V or IS3-like insertion sequences. Among VanA elements with alterations downstream of vanX, seven lacked vanY, one lacked both van Y and vanZ, and ten had copies of insertion sequence IS 1216V between vanX and vanY. All VanA elements of group D (from geographically and temporally diverse enterococci) were characterized by the presence of an IS 1216V/IS3-like/orf1 complex and a point mutation in vanX, both of which were absent from the other 23 groups of VanA elements. This finding is consistent with the dissemination of a stable resistance element. We conclude that L-PCR RFLP analysis, combined with DNA hybridization, merits further development for studying the evolution and epidemiology of VanA resistance elements in enterococci.