Genetic rearrangements of TN1546-like elements in vancomycin-resistant Enterococcus faecium isolates collected from hospitalized patients over a seven-year period

Molecular epidemiology of vancomycin-resistant enterococci isolated from non-tertiary-care and tertiary-care hospitals in Korea

This study compared the molecular characteristics of vancomycin-resistantEnterococcus faecium(VREF) isolates recovered from 20 non-tertiary-care hospitals (36 isolates) and three tertiary-care hospitals (26 isolates) in diverse geographical areas of Korea from October 2010 to April 2011. All isolates carried thevanAgene only, but 42% and 73% of non-tertiary and tertiary-care isolates expressed the VanB phenotype (teicoplanin minimum inhibitory concentration ⩽16 μg/ml). All isolates harboured insertion sequences, IS1542and IS1216V, within Tn1546. The isolates from tertiary-care hospitals tended to have reduced Tn1546lengths by deletion of sequences adjacent to IS elements. Multilocus sequence typing revealed eight sequence types within clonal complex 17 (CC17), but DNA fingerprinting by rep-PCR did not show clonal relatedness between the intra- and inter-hospital isolates. These results suggest thatvanA, which has prevailed in tertiary-care hospitals of Korea since the 1990s, had been transferred horizontally to non-tertiary-care hospitals while the genetic rearrangement driven by evolutionary adaptation to adverse environments may have occurred in tertiary-care hospitals.

Comparison of genetic epidemiology of vancomycin-resistant Enterococcus faecium isolates from humans and poultry

This study was conducted to investigate the molecular characteristics and genetic relatedness of vancomycin-resistant Enterococcus faecium (VREF) isolates obtained from humans and poultry in Korea. A total of 147 VREF isolates from humans (71 clinical isolates) and poultry (76 isolates) in Korea were compared with respect to their antibiotic susceptibilities, organization of the Tn1546 transposon element, detection of virulence genes (esp and hyl), pulsed-field gel electrophoresis (PFGE) typing and multilocus sequence typing (MLST). All of the human and poultry isolates had the vanA gene and 11.3% (8/71) of the clinical isolates showed the VanB phenotype/vanA genotype. PCR mapping of the Tn1546 elements was different for isolates of the two groups: human isolates were classified into five transposon types, whereas all poultry isolates were identical to Tn1546 of E. faecium strain BM4147. The esp gene was detected in both human (93.0%, 66/71) and poultry (26.3%, 20/76) isolates, as was the hyl gene (human isolates: 80.3%, 57/71; poultry isolates: 26.3%, 20/76). Using MLST, the 71 human isolates could be divided into ten sequence types (STs) belonging to clonal complex (CC) 17 (except for one singleton). The 76 poultry isolates were categorized into 14 STs and 88.2% (67/76) of the poultry isolates belonged to CC26. PFGE typing of the human isolates demonstrated diverse PFGE profiles among the strains. However, the PFGE patterns of the poultry isolates were possibly related to the strains collected from individual farms. These data suggest that epidemic clonal groups of human and poultry VREFs in Korea have evolved through different evolutionary processes.

Molecular epidemiology of vancomycin-resistant Enterococcus faecium bloodstream infections among patients with neutropenia over a 6-year period in South Korea

Over a 6-year period (March 2000-February 2006), there were 60 vancomycin-resistant Enterococcus faecium (VREF) bloodstream infections (BSIs) in a hematology unit, accounting for 83.3% of all VREF BSIs in the hospital. We investigated 49 VREF isolates causing BSIs in patients with neutropenia to understand the molecular epidemiology at this unit. All isolates had the vanA genotype. Pulsed-field gel electrophoresis typing revealed high clonal diversity (23 types with nine clusters comprising 35 isolates) and 1 predominant type, type A (14/49, 28.6%), persisted at this unit throughout the study period, suggesting the clonal spread of this endemic strain by cross-contamination. Tn1546 types were less heterogeneous, with five main Tn1546 types, two of which (types I and IV) accounted for 67.4% of isolates. This indicates that in addition to clonal spread, the horizontal transfer of Tn1546 played a major role in the nosocomial dissemination of vancomycin resistance. The genetic diversity of VREF increased over time, implying an increasing influx of new strains into the unit and genetic changes, possibly attributable to the horizontal transfer of diverse Tn1546 types. Despite such diversity, all the isolates belonged to clonal complex 17, which is the epidemic clone worldwide, enriched with the esp (35/49, 71.4%) and hyl (24/49, 48.9%) virulence genes. This hospital-adapted clone has become endemic and is well suited to causing BSIs in patients with neutropenia in this unit.

Isolation of Tn1546-like elements in vancomycin-resistant Enterococcus faecium isolated from wood frogs: an emerging risk for zoonotic bacterial infections to humans

AIM

Isolation and characterization of vancomycin-resistant enterococci (VRE), mainly Enterococcus faecium, from the faecal pellet of wood frogs (Rana sylvatica).

METHODS AND RESULTS

The frog VRE isolates were tested for their susceptibility to various antibiotics and were found resistant to ampicillin (Am), chloramphenicol (Cm), erythromycin (Em), gentamicin (Gm), tetracycline (Tc), teicoplanin (Tp) and vancomycin (Vn). The linkage of multiple antibiotic resistances to Em, Tc, Tp and Vn was observed in 84% of resistant Ent. faecium. Inducible antibiotic resistance (MIC ≥ 512 μg ml(-1) ) to Vn was also detected in these isolates. PCR analysis revealed the presence of vanA in all strains, and none of the strains were positive for vanB, indicating the existence of vanA phenotype. Furthermore, the PCR-RFLP analysis of the frog vanA amplicon with PstI, BamHI and SphI generated identical restriction patterns similar to Tn1546-like elements found in human VRE isolates. DNA homoduplex analysis also confirmed that vanA from the frog VRE has DNA sequence homology with the vanA of Tn1546-like elements of human and animal isolates. Blastx analysis of frog vanA sequence showed similarities with protein sequences generated from protein database of Vn-resistant Ent. faecium, Baccilus circulans, Paenibacillus apiarius and Oerskovia turbata isolates. Horizontal transfer of Vn resistance was not detected in frog isolates as revealed by filter mating conjugal experiment.

CONCLUSIONS

In summary, our results demonstrated that wood frogs carry Vn-resistant bacteria, and resistance genes (vanA) are located on Tn1546-like elements.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study highlights a previously less recognized role of amphibians as sentinels for multidrug-resistant bacteria and alerts the public health workers for an emerging risk of zoonotic bacterial infections to humans.