Clinical implications of vancomycin-resistant Enterococcus faecium (VRE) with VanD phenotype and vanA genotype

Objectives: To investigate the clinical implications of vancomycin-resistant Enterococcus faecium (VRE) with VanD phenotype and vanA genotype (VanD-vanA VRE). Methods: We tested in vitro and in vivo efficacies of teicoplanin against VanD-vanA VRE strains. Change in teicoplanin MICs was monitored during incubation with teicoplanin. In vitro and in vivo time-kill assay and survival analysis using a mouse peritonitis model were performed. Results: Teicoplanin MICs of VanD-vanA VRE strains increased to 128 mg/L within 48 h when they were cultured with 120 mg/L teicoplanin. In vitro and in vivo time-kill assay showed that VanD-vanA VRE strains were not eliminated by 120 mg/L teicoplanin in contrast to vancomycin-susceptible E. faecium and VanD-vanB strains. The survival rate of mice infected with VanD-vanA VRE strains treated with teicoplanin was comparable with that of untreated mice. Conclusion: Data suggest that teicoplanin would fail in the treatment of VanD type VRE infections if the strains contained the vanA gene, which cannot be detected in the clinical microbiology laboratory.