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

To investigate the clinical implications of vancomycin-resistant Enterococcus faecium (VRE) with VanD phenotype and vanA genotype (VanD-vanA VRE).

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.

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.

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.