No abstract

We report on a detailed study on the molecular diversity and evolutionary relationships of Tn1546-like elements in vancomycin-resistant enterococci (VRE) from humans and animals. Restriction fragment length polymorphism (RFLP) analysis of the VanA transposon of 97 VRE revealed seven different Tn1546 types. Subsequent sequencing of the complete VanA transposons of 13 VRE isolates representing the seven RFLP types followed by sequencing of the identified polymorphic regions in 84 other VanA transposons resulted in the identification of 22 different Tn1546derivatives. Differences between the Tn1546 types included point mutations in orf1, vanS,vanA, vanX, and vanY. Moreover, insertions of an IS1216V-IS3-like element inorf1, of IS1251 in the vanS-vanHintergenic region, and of IS1216V in thevanX-vanY intergenic region were found. The presence of insertion sequence elements was often associated with deletions in Tn1546. Identical Tn1546 types were found among isolates from humans and farm animals in The Netherlands, suggesting the sharing of a common vancomycin resistance gene pool. Application of the genetic analysis of Tn1546 to VRE isolates causing infections in hospitals in Oxford, United Kingdom, and Chicago, Ill., suggested the possibility of the horizontal transmission of the vancomycin resistance transposon. The genetic diversity in Tn1546 combined with epidemiological data suggest that the DNA polymorphism among Tn1546 variants can successfully be exploited for the tracing of the routes of transmission of vancomycin resistance genes.

In order to determine the prevalence of vancomycin-resistant enterococci (VRE) in The Netherlands, 624 hospitalized patients from intensive care units or hemato-oncology wards in nine hospitals and 200 patients living in the community were screened for VRE colonization. Enterococci were found in 49% of the hospitalized patients and in 80% of the patients living in the community. Of these strains, 43 and 32%, respectively, were Enterococcus faecium. VRE were isolated from 12 of 624 (2%) and 4 of 200 (2%) hospitalized patients and patients living in the community, respectively. PCR analysis of these 16 strains and 11 additional clinical VRE isolates from one of the participating hospitals revealed 24 vanA gene-containing, 1 vanB gene-containing, and 2 vanC1 gene-containing strains. All strains were cross-resistant to avoparcin but were sensitive to the novel glycopeptide antibiotic LY333328. Genotyping of the strains by arbitrarily primed PCR and pulsed-field gel electrophoresis revealed a high degree of genetic heterogeneity. This underscores a lack of hospital-driven endemicity of VRE clones. It is suggested that the VRE in hospitalized patients have originated from unknown sources in the community. Enterococcus spp. have recently emerged as important nosocomial pathogens (35). According to the data from the National Nosocomial Infections Surveillance System, enterococci are the fourth leading cause of nosocomial infections in the United States (12). Enterococcal infections that have frequently been reported include urinary tract infections, bacteremia, endocarditis, intra-abdominal infections, and surgical wound infections (27). Enterococcus faecalis is commonly isolated from the human gastrointestinal tract, whereas Enterococcus faecium is less frequently isolated from that site (31). This latter species, however, is noted for its antimicrobial resistance. Vancomycin-resistant E. faecium (VREF) strains have emerged in a setting of increasing high-level resistance of enterococci to penicillins and aminoglycosides (28). During the last few years, nosocomial outbreaks due to VREF have been described (17, 25). The emergence of VREF has raised serious concerns (28), and in response, the Hospital Infections Control Practices Advisory Committee (HICPAC), in collaboration with the Centers for Disease Control and Prevention, has developed recommendations for preventing the spread of vancomycin-resistant enterococci (VRE) (18). Given the concern that vancomycin resistance genes may transfer from enterococci to Staphylococcus aureus, a phenomenon that has been observed in vitro (31), control measures have already been proposed, should vancomycin-resistant S. aureus strains eventually arise (10). MATERIALS AND METHODS Prevalence study. Five Dutch university hospitals in Rotterdam, Utrecht, Nijmegen, and Amsterdam and four regional teaching hospitals in Breda and Tilburg participated in the study. Six hundred twenty-four patients who were hospitalized in the following wards were screened for gastrointestinal carriage of VRE...

Campylobacter jejuni isolates (n ‫؍‬234