d-Ala-d-Ser VanN-Type Transferable Vancomycin Resistance in Enterococcus faecium

Abstract

ABSTRACTEnterococcus faeciumUCN71, isolated from a blood culture, was resistant to low levels of vancomycin (MIC, 16 μg/ml) but susceptible to teicoplanin (MIC, 0.5 μg/ml). No amplification was observed with primers specific for the previously described glycopeptide resistance ligase genes, but a PCR product corresponding to a gene calledvanNwas obtained using degenerate primers and was sequenced. The deduced VanN protein was related (65% identity) to thed-alanine:d-serine VanL ligase. The organization of thevanNgene cluster, determined using degenerate primers and by thermal asymmetric interlaced (TAIL)-PCR, was similar to that of thevanCoperons. A single promoter upstream from the resistance operon was identified by rapid amplification of cDNA ends (RACE)-PCR. The presence of peptidoglycan precursors ending ind-serine andd,d-peptidase activities in the absence of vancomycin indicated constitutive expression of the resistance operon. VanN-type resistance was transferable by conjugation toE. faecium. This is the first report of transferabled-Ala-d-Ser-type resistance inE. faecium.