Six VanB phenotype-vanA genotype isolates of Enterococcus faecium with heterogeneous expression of teicoplanin resistance which gave rise to an outbreak at a Korean tertiary care teaching hospital have IS1216V in the coding region of vanS. This could be the underlying cause of the VanB phenotype-vanA genotype with heterogeneous expression of teicoplanin resistance.

The heterogeneity of Tn1546 results from point mutations, deletions, and the integration of insertion sequence (IS) elements. Among these variations, the presence of IS elements accounts for much of the heterogeneity. Such a rearrangement could play a key role in the evolution of the vanA gene cluster, and hence, it may modify its transferability. In this study, we characterized the consequence of Tn1546 in vanA-containing Enterococcus faecium isolates collected from patients over time. From 1998 to 2004, 57 vanA-containing E. faecium isolates were collected from hospitalized patients at Ajou University Hospital in Korea. PCR amplification of internal regions of Tn1546 was performed, and both DNA strands were directly sequenced by the dideoxy termination method. All isolates were divided into three main types, including the prototype, according to the distribution of IS elements integrated into Tn1546 elements. Type I was characterized by an IS1542 insertion in the orf2-vanR intergenic region and an IS1216V insertion in the vanX-vanY intergenic region. Type II was represented by the presence of two copies of IS1216V at the 3 end of IS1542 and in the vanX-vanY intergenic region, as well as IS1542 in the orf2-vanR intergenic region. Seventeen strains isolated from 1998 to 2000 represented type I, and 38 strains isolated from 2000 to 2004 represented type II. The remaining two isolates were the prototype. The tendency for the rearrangement of Tn1546 was that the sequences were shortened as time passed, especially at the left or the right end, and hence, this could gradually modulate their transferability.

In July 2010, we identified an outbreak of vancomycin-resistant enterococci (VRE) in our 26-bed neonatal intensive care unit. We performed an epidemiological investigation after clinical cultures of 2 neonates were positive for VRE. Identification, susceptibility testing, and molecular characterization were performed. Cultures of 3 surveillance stool samples of inpatients and 5 environmental samples were positive for VRE. All isolates were identified as Enterococcus faecium containing the vanA gene. Two distinct clones were identified by performing pulsed-field gel electrophoresis. The 2 clones exhibited different pulsotypes, but they represented identical Tn1546 types. Two sequence types, ST18 and ST192, were identified among all of the isolates with multilocus sequence typing. Our investigation determined that the outbreak in the neonatal intensive care unit was caused by 2 genetically different clones. The outbreak may have occurred through clonal spread and horizontal transfer of the van gene.

No abstract

No abstract