Molecular Characterization of Vancomycin-Resistant Enterococci Isolates

Abstract

To investigate the prevalence and genotype of vancomycin-resistant enterococci (VRE)faecium and faecalis isolates. Thirty-eight non duplicate vancomycin -resistant enterococci isolates were collected from 2003 to 2007 in Beijing Chaoyang hospital. The prevalence of VRE was analyzed using WHONET software. These strains were processed by brain heart infusion agar screening in the presence of vancomycin (6 mg/L), and were analyzed for genotypic characteristics using multiplex PCR. The homology of the isolates was determined by pulsed-field gel electrophoresis (PFGE). Most VRE strains were isolated from the ICU patients (34.2% , 13/38). The vancomycin resistance rate (vancomycin MIC> or =16 mg/L) was 2.6% in 2003, 1.8% in 2004, 0.7% in 2005, 6. 8% in 2006, and 3.3% in Jan - Mar 2007. Fifteen vancomycin-resistant Enterococci faecalis isolates were identified as vanB genotype by PCR and sequencing. (the vancomycin MIC ranged from 16 to 48 mg/L and the teicoplanin MIC ranged from 0.38 to 0.5 mg/L). The vanA gene was confirmed by PCR and sequencing in twenty-three vancomycin-resistant Enterococcus faecium (vancomycin MIC > or =256 kg/L, teicoplanin MIC = 2-32 mg/L). Twelve vancomycin-resistant Enterococcus faecium isolates showed incongruence between phenotype and genotype for glycopeptides resistance (vanA genotype and vanB phenotype). The PFGE analysis revealed 10 different PFGE types. Fourteen vancomycin-resistant Enterococci faecalis isolates belonged to the same clone. 21 vancomycin-resistant Enterococci faecium isolates belonged to 9 PFGE types. The four most prevalent clones was A, D, E and F. The VRE strains isolated from Beijing Chaoyang Hospital belong to vanA and vanB genotypes. Vancomycin -resistant Enterococci faecalis is monoclonal, and vancomycin-resistant Enterococci faecium is polyclonal. Some of the vancomycin-resistant Enterococcus faecium isolates show incongruence between phenotype and genotype.