Distribution of streptogramin resistance determinants and clonality analysis among Enterococcus faecium from 1999 to 2004 at a teaching hospital in Taiwan

While the antibiotic streptogramin Synercid hadn’t been approved for clinical use, prevalence of resistance to Synercid was demonstrated among 51% of vancomycin-resistant Enterococcus faecium (VREF) isolates in the year 2000 in Taiwan. These observations led to essentiality of investigation of clonal relationships and the molecular determinants among these isolates.
A total of 119 E. faecium strains were subjected for study, including 115 clinical isolates from National Taiwan University Hospital between 1999 to 2004, 3 chicken isolates from traditional markets and 1 ATCC strain. Molecular identification confirmed E. faecium strains before determination of MICs against vancomycin and Synercid. Results of Multiplex PCR assay showed all VREF strains were vanA type.
Clonality analysis by PFGE under unweighted-pair-group and arithmetic averages (UPGMA) methods and Gel-compar II software was performed. Isolates having identical or similar profiles, differing by six or fewer bands were assigned to the same cluster and defined the cluster similarity cut-off as 80%. The 119 E. faecium isolates were grouped into 17 clusters, each containing 1 to 56 related isolates. Cluster A strains which was the predominant PFGE type were VREF and showed main clonality spreading during the period studied. Sparse nosocomial infections among VREF and Synercid-resiatant E. faecium (SREF) were observed. In comparison, the three animal isolates showed low similarity to clinical E. faecium isolates. PCR screening for the streptogramin resistance determinants erm(B), msr(C), vgb(A), vat(D), and vat(E) basically could not account for streptogramin resistance. The erm(B) and msr(C) were identified among 98.3% and 47.1% of test isolates whereas vgb(A) or vat(D) and vat(E) were not detected. Chi-square analysis showed erm(B) and msr(C) genes are not significantly related with Synercid phenotypes. The current results showed SREF strains are commonly identified among clinical isolates. Most of the isolates formed clusters. Only sparse nosocomial SREF and VREF disseminations were observed. The potential mechanism of Synecid resistance remains largely uncharacterized in these isolates.