Role of Transposon Tn5482in the Epidemiology of Vancomycin-ResistantEnterococcus faeciumin the Pediatric Oncology Unit of a New York City Hospital

Abstract

During a 36-month period between 1993 and 1995 in the Pediatric Oncology Unit of Memorial Sloan Kettering Cancer Center, 74 patients experienced episodes of infection or colonization caused by vancomycin-resistant enterococci (VRE). Characterization of the 74 bacterial isolates by microbiological and molecular techniques (pulsed-field gel electrophoresis and hybridization with DNA probes specific for the vanA and vanB genes and for IS1251) identified 73 Enterococcusfaecium and one Enterococcusfaecalis (vanB) among the primary VRE isolates. Most (69/73) of the E. faecium isolates carried vanA and four isolates, the vanB gene complex. The overwhelming majority (67/69) of the vanA -positive isolates also gave hybridization signal for IS1251, indicating the presence of the newly described conjugative transposon Tn5482. No hybridization with IS1251 was obtained with the four vanB-carrying isolates. About 30% of the vanA-positive strains (23/69) were represented by PFGE subtype variants of a single clone, most isolates of which were recovered during a 4-month period between April to June of 1994. The larger portion of the vanA-carrying VRE represented by close to 70% of the isolates (46/69) belonged to as many as 37 different clonal types, indicating tremendous genetic diversity. Among 67 of the 69 vanA-carrying isolates, the localization of the Tn5482-associated vanA gene complex could be unequivocally identified either on the chromosome (40/69) or in plasmids (27/69). Transconjugants recovered from filter mating experiments using either a chromosomally located or plasmid-borne vanA donor strain and a single vancomycin-susceptible strain of either E. faecium or E. faecalis were analyzed by molecular typing techniques. Seven out of 10 independent transconjugants recovered from the same cross showed extensive differences in PFGE pattern and also in the localization of the vanA hybridizing DNA fragment transferred from the common VRE donor with chromosomally located vanA. The observations suggest that the extensive genetic diversity observed among the clinical isolates of VRE may be generated during conjugation between vancomycin-resistant and -susceptible enterococcal isolates. The observations also suggest that the epidemic spread of VRE in the United States may be linked to the frequent presence of Tn5482 among the American isolates.

Diversity of Tn 1546 and Its Role in the Dissemination of Vancomycin-Resistant Enterococci in Portugal

“…Horizontal transfer of conjugative plasmids containing Tn1546 seems to have played a relevant role in the recent increase of VRE in Portugal, as vanA was plasmid located in most VRE isolates studied and specific plasmids containing the most prevalent Tn1546 variants were identified in representative distinct clones collected from different cities and years (13). Nevertheless, the role of prevalent and persistent E. faecalis and E. faecium strains in the maintenance of the resistance by acquiring different genetic elements must not be underestimated, highlighting the complex epidemiology associated with successful spread of multidrug-resistant enterococci, as illustrated in Poland and the United States, where both successful plasmids and prevalent clones contributed to endemicity (11,21,22). Plasmid persistence has been described in areas with both high and low antibiotic selective pressure, as in the United States versus Norway or Denmark, suggesting that factors other than antibiotic pressure might be important in VRE maintenance and epidemiology (17,20).…”

Frequent Transmission of Enterococcal Strains between Mechanically Ventilated Patients Treated at an Intensive Care Unit

“…All collected enterococcal isolates (n ϭ 170) were further analyzed by pulsed-field gel electrophoresis (PFGE). Chromosomal DNA from the enterococcal isolates was prepared as described by De Lencastre et al (4) with some modifications as previously described (12). The DNAcontaining disks were restricted overnight with SmaI (Promega Corporation, Madison, Wis.) at ϩ37°C and loaded in a gel run for 20 h at ϩ14°C in a contour-clamped homogenous electric field apparatus (GenePathsystem; Bio-Rad Laboratories, Hercules, Calif.).…”

Bloodstream Isolates of Enterococcus faecium Enriched with the Enterococcal Surface Protein Gene, esp , Show Increased Adhesion to Eukaryotic Cells

“…Thirty fecal E. faecium strains collected pretreatment from 30 healthy donors participating in clinical trials conducted in 1998 (13,16) and two E. faecium strains from probiotic products, the SF68 strain (Ventrux, AB Cernelle, Angelholm, Sweden) and the Causido-derived E. faecium strain (Gaio; MD Foods, Aarhus, Denmark), were also included. All blood culture isolates were genotyped with pulsed-field gel electrophoresis (4,11). To avoid repeated analyses of nosocomial clones, only one isolate of each unique banding pattern was included.…”