Clinical and Microbiological Characteristics of Vancomycin-Resistant Enterococci with the VanD Phenotype and vanA Genotype

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Vancomycin-resistant enterococci (VRE) strains with the VanD phenotype and vanA genotype (VanD-vanA) have been reported in Asian countries. The VanD phenotype is characterized by low-level resistance to vancomycin and susceptibility or intermediate resistance to teicoplanin. We retrospectively determined the risk factors, clinical outcomes, and virulence factors for VanD-vanA VRE (20 patients colonized with Enterococcus faecium) compared to VanA-vanA VRE (20 patients colonized with E. faecium). Multiple VRE colonizations and recent glycopeptide use were related to the presence of the VanA phenotype. There were no significant differences between patients colonized with VanD-vanA VRE and VanA-vanA VRE for duration of hospital stay, duration of intensive care unit stay, or hospital mortality. The esp gene was identified from all enterococci, while 90% of VanD-vanA VRE isolates and 95% of VanA-vanA VRE isolates were positive for the hyl gene. VanA-vanA VRE was subsequently isolated from sequential samples in 8 of 20 patients (40%) with VanD-vanA VRE. All of these patients had received glycopeptides during the interval between sample collection, and 2 of 8 paired isolates (VanD-vanA VRE and VanA-vanA VRE) were closely related subtypes according to pulsed-field gel electrophoresis analysis. In conclusion, VanD-vanA VRE isolates might represent an unstable, heterogeneous population that can convert to the VanA phenotype after exposure to glycopeptides.