vanM , a New Glycopeptide Resistance Gene Cluster Found in Enterococcus faecium

Since glycopeptide-resistant enterococci (GRE) were reported in 1988, they have appeared in hospitals worldwide. Seven van gene cluster types ( vanA , vanB , vanC , vanD , vanE , vanG , and vanL ) are currently known. We investigated a clinical strain of Enterococcus faecium Efm-HS0661 that was isolated in 2006 from an inpatient with intra-abdominal infection in Shanghai. It was resistant to most antimicrobials, including vancomycin (MIC, >256 μg/ml) and teicoplanin (MIC, 96 μg/ml). Glycopeptide resistance could be transferred to E . faecium BM4105RF by conjugation. The donor and its transconjugant were negative by PCR for the known van genes. By cloning and primer walk sequencing, we discovered a novel van gene cluster, designated vanM . The vanM ligase gene was 1,032-bp in length and encoded a 343-amino-acid protein that shared 79.9, 70.8, 66.3, and 78.8% amino acid identity with VanA, VanB, VanD, and VanF, respectively. Although the vanM DNA sequence was closest to vanA , the organization of the vanM gene cluster was most similar to that of vanD . Upstream from the vanM cluster was an IS 1216- like element, which may play a role in the dissemination of this resistance determinant. Liquid chromatography-mass spectrometry analysis of peptidoglycan precursors extracted from the VanM-type strain Efm-HS0661 treated with vancomycin or teicoplanin revealed a modified precursor (UDP- N -acetylmuramic acid [MurNAc]-tetrapeptide- d -Lac), indicating that VanM, like VanA, confers glycopeptide resistance by the inducible synthesis of precursor ending in d -Ala- d -Lac.