GENETIC-LINKAGE AND COTRANSFER OF A NOVEL, VANB-CONTAINING TRANSPOSON(TN5382) AND A LOW-AFFINITY PENICILLIN-BINDING PROTEIN-5 GENE IN A CLINICAL VANCOMYCIN-RESISTANT ENTEROCOCCUS-FAECIUM ISOLATE

Mechanisms for the intercellular transfer of VanB-type vancomycin resi stance determinants and for the almost universal association of these determinants with those for high-level ampicillin resistance remain po orly defined. We report the discovery of Tn5382, a ca, 27-kb putative transposon encoding VanB-type glycopeptide resistance in Enterococcus faecium. Open reading frames internal to the right end of Tn5382 and d ownstream of the vanX(B) dipeptidase gene exhibit significant homology to genes encoding the excisase and integrase of conjugative transposo n Tn916, The ends of Tn5382 are also homologous to the ends of Tn916, especially in regions bound by the integrase enzyme, PCR amplification experiments indicate that Tn5382 excises to form a circular intermedi ate in E. faecium. Integration of Tn5382 in the chromosome of E, faeci um C68 has occurred 113 bp downstream of the stop codon for the pbp5 g ene, which encodes high-level ampicillin resistance in this clinical i solate. Transfer of vancomycin, ampicillin, and tetracycline resistanc e from C68 to an E, faecium recipient strain occurs at low frequency i n vitro and is associated with acquisition of a 130- to 160-kb segment of DNA that contains Tn5382, the pbp5 gene, and its putative represso r gene, psr, The interenterococcal transfer of this large chromosomal element appears to be the primary mechanism for vanB operon spread in northeast Ohio, These results expand the known family of Tn916-related transposons, suggest a mechanism for vanB operon entry into and disse mination among enterococci, and provide an explanation for the nearly universal association of vancomycin and high-level ampicillin resistan ce in clinical E, faecium strains.