Antibiotic activity against urinary tract infection (UTI) isolates of vancomycin-resistant enterococci (VRE): results from the 2002 North American Vancomycin Resistant Enterococci Susceptibility Study (NAVRESS)

Background: The purpose of this study was to assess the prevalence of vancomycin-resistant enterococci (VRE) in urinary isolates in North America, and the activity of various antibiotics against VRE. Materials and methods: Twenty-eight medical centres in the United States and 10 centres in Canada assessed the prevalence of VRE in urinary isolates in 2002. Each study site was asked to collect up to a maximum of 50 consecutive VRE (Enterococcus faecium, Enterococcus faecalis only) urinary isolates. Susceptibility was determined by NCCLS broth microdilution. The prevalence of vanA and vanB resistance genotypes was determined by multiplex PCR. Results: From the 28 US medical centres, a total of 697 VRE (616 [88.4%] E. faecium and 81 [11.6%] E. faecalis) were received. Approximately 75% of all VRE (E. faecium and E. faecalis) isolates demonstrated a VanA phenotype (resistance to both vancomycin and teicoplanin). PCR detection of vanA and vanB resistance determinants showed that the vanA genotype was present in 584 of 697 (83.8%) VRE isolates, whereas 113 (16.2%) isolates possessed the vanB gene. The most active agents were linezolid, nitrofurantoin and chloramphenicol, with 0.3%, 0.6% and 2.4% resistance, respectively. The majority (77.8%) of vancomycin-resistant E. faecium isolates displayed the VanA phenotype, and 538 of these 616 (87.3%) isolates were PCR-positive for vanA; the vanB genotype was detected in 78 (12.7%) isolates. Resistance was lowest with linezolid, chloramphenicol and nitrofurantoin at 0.3%, 0.3% and 0.5%, respectively. Only three genetically indistinguishable vanA-positive E. faecium were isolated from the 10 Canadian medical centres. Conclusion: VRE urinary isolates are common in the United States, are primarily of the vanA genotype and are very susceptible to linezolid, nitrofurantoin and chloramphenicol. In Canada, VRE urinary isolates remain uncommon.