Use of primers selective for vancomycin resistance genes to determine van genotype in enterococci and to study gene organization in VanA isolates.

Vancomycin resistance in enterococci is an emerging therapeutic problem. Resistance is not always detected by standard microbiological methods. Oligonucleotide primers for PCR were designed to target amplification of defined regions of genes of the vanA cluster, as well as vanB and vanC1. These primers correctly identified 30 vancomycin-resistant isolates tested (17 VanA, 7 VanB, and 6 Enterococcus gallinarum). No amplification was observed with Enterococcus casseliflavus or vancomycin-susceptible strains. Using PCR and Southern blotting, we found that all 17 VanA isolates had orf-1, orf-2, vanR, vanS, vanH, vanA, and vanY genes in the same sequence and that the intergenic distances in the vanR-vanA segments were the same. The described methods should be applicable to the rapid detection of the different vancomycin resistance genotypes in enterococci.