Molecular analysis of diverse elements mediating VanA glycopeptide resistance in enterococci

Differences were examined among 24 distinct elements mediating VanA-type gl ycopeptide resistance in enterococci isolated from hospital patients and no n-human sources in the UK. The methods used included long-PCR restriction f ragment length polymorphism (L-PCR RFLP) analysis and DNA hybridization. Al l elements had conserved vanRSHAX genes, but variation occurred upstream of vanR and downstream of vanX. Twenty-one VanA elements had significant alte rations upstream of vanR in the transposition genes orf1 and orf2: either p arts of these genes were absent or they were disrupted by IS1216V or IS3-li ke insertion sequences. Among VanA elements with alterations downstream of vanX, seven lacked vanY, one lacked both vanY and vanZ, and ten had copies of insertion sequence IS1216V between vanX and vanY. All VanA elements of g roup D (from geographically and temporally diverse enterococci) were charac terized by the presence of an IS1216V/IS3-like/orf1 complex and a point mut ation in vanX, both of which were absent from the other 23 groups of VanA e lements. This finding is consistent with the dissemination of a stable resi stance element. We conclude that L-PCR RFLP analysis, combined with DNA hyb ridization, merits further development for studying the evolution and epide miology of VanA resistance elements in enterococci.