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

Abstract

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.