Characterization of the vanD glycopeptide resistance gene cluster from Entercoccus faecium BM4339

VanD-type resistance to glycopeptides in Enterococcus faecium BM4339 is due to constitutive synthesis of D-alanyl-D-lactate-terminating peptidoglycan precursors (B. Perichon, P. Reynolds, and P. Courvalin, Antimicrob. Agents Chemother, 41:2016-2018, 1997), The sequence of a 5,780-bp fragment was determined and revealed six open reading frames. The 3' distal part encoded the VanH(D) dehydrogenase, the VanD ligase, and the VanX(D) DD dipeptidase, which were highly similar to the corresponding proteins in VanA and VanB types of resistance. The deduced VanY(D) protein was homologous to penicillin-binding proteins that display DD-carboxypeptidase activity. The 5' end coded for the putative VanR(D)-VanS(D) two-component regulatory system. Due to a frameshift mutation in the chromosomal ddl gene, BM4339 produced an impaired D-alanine:D-alanine ligase, However, since expression of the resistance genes is constitutive, growth of E. faecium BM4339 was not dependent on the presence of glycopeptides in the culture medium.