Journal of Bacteriology, September 1998, p. 4426-4434, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Department of Medicine and Research Service,
Received 16 January 1998/Accepted 10 June 1998
Mechanisms for the intercellular transfer of VanB-type vancomycin
resistance determinants and for the almost universal association of
these determinants with those for high-level ampicillin resistance remain poorly 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 downstream of the
vanXB dipeptidase gene exhibit significant
homology to genes encoding the excisase and integrase of conjugative
transposon 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 intermediate in
E. faecium. Integration of Tn5382 in the
chromosome of E. faecium C68 has occurred 113 bp downstream
of the stop codon for the pbp5 gene, which encodes high-level ampicillin resistance in this clinical isolate. Transfer of
vancomycin, ampicillin, and tetracycline resistance from C68 to an
E. faecium recipient strain occurs at low frequency in
vitro and is associated with acquisition of a 130- to 160-kb segment of
DNA that contains Tn5382, the pbp5 gene, and
its putative repressor 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 dissemination among enterococci, and provide an explanation for the
nearly universal association of vancomycin and high-level ampicillin
resistance in clinical E. faecium strains.
*
Corresponding author. Mailing address: Infectious
Diseases Section 1110(W), VA Medical Center, 10701 East Blvd.,
Cleveland, OH 44106. Phone: (216) 791-3800, ext. 4399. Fax: (216)
231-3482. E-mail: Lbr{at}po.cwru.edu.
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