Antimicrobial Agents and Chemotherapy, January 2001, p. 367-368, Vol. 45, No. 1
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.45.1.367-368.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Prevalence of the vanB2 Gene Cluster in VanB
Glycopeptide-Resistant Enterococci in the United Kingdom and the
Republic of Ireland and Its Association with a
Tn5382-Like Element
The vanB gene cluster of enterococci confers
resistance to vancomycin but not teicoplanin (4). In the
United Kingdom, this cluster is found in approximately 15% of
glycopeptide-resistant enterococci from hospitalized patients
(8), although proportions as high as 64 and 90% have been
reported in some hospitals (9, 11). Three subtypes, based
on nucleotide variability, have been designated vanB1,
vanB2, and vanB3 (2, 10),
respectively, and have been found within different transposons
(3). We previously analyzed vanB-mediated
resistance in isolates from Scotland, showing that 28 (88%) of 32 belonged to subtype vanB2 (7). In this study we
examined the prevalence of vanB subtypes among enterococci isolated in the United Kingdom and the Republic of Ireland and investigated whether vanB was located on a transferable element.
A total of 204 vanB enterococcal isolates, isolated between
1989 and 1999 from patients in 59 different hospitals in England, Wales, and Scotland and from a single hospital in the Republic of
Ireland, were examined. Nucleotide sequencing and HhaI
digestion of a fragment of the vanB gene was used to
distinguish between the vanB1, vanB2, and
vanB3 gene clusters (7). Based on their vanB-HhaI restriction fragment length polymorphism (RFLP)
profiles, 202 (99%) isolates contained vanB2. The presence
of vanB1 in two isolates was confirmed by sequence analysis.
vanB2 has been associated with the ca. 27-kb
conjugative transposon, Tn5382 (1, 3), and the
closely related Tn1549 transposon (5).
Therefore, we selected 28 vanB2 isolates from the above collection (19 Enterococcus faecium isolates and 8 E. faecalis isolates from England and Wales, as well as 1 E. casseliflavus isolate from Dublin, Republic of Ireland), together
with the 28 vanB2 E. faecium isolates from Scotland
(7), to examine whether the vanB2 gene cluster
was associated with a similar element. E. faecium strain
C68, previously shown to carry the Tn5382 element (1), was kindly provided by L. B. Rice for use as a
positive control. Using primers specific to sequences in the left end
of Tn5382 (5'-ACG CCA TGC TAT TTA CTT CCG GC-3' and 5'-GTT
CTT ATT CCG CAG GTG GTG ATT-3' [1]), a 311-bp PCR fragment was
generated from strain C68, and a similarly sized fragment was generated from each of the 56 selected isolates. A second set of primers (5'-TTG
CAT GGT GTT CGT TGG-3' and 5'-CGG CAT CAA CGC CTT TAG-3') was used to
amplify a 1,581-bp fragment containing vanXB2
and part of the right end of Tn5382 from strain C68. A
similarly sized fragment from each of the 56 isolates in this study was
also amplified, suggesting that, in all cases, the vanB2
gene cluster was associated with sequences similar to those previously
seen in Tn5382.
In several VanB strains of E. faecium isolated in the United
States, Tn5382 contains insertion sequences and is located
directly downstream of pbp5, which encodes a low-affinity
penicillin-binding protein responsible for high-level ampicillin
resistance in E. faecium isolates (1, 3, 6).
RFLP analysis of long PCR fragments spanning
vanSB2-vanXB2 (7) from
the 56 selected isolates showed that none contained
ISEnfa200 (3) or any other additional DNA.
Further PCR studies showed that Tn5382 was not located
downstream of pbp5 in any of the 47 E. faecium isolates.
Pulsed-field gel electrophoresis analysis of SmaI-digested
DNA from the 56 isolates revealed 35 different types (12).
Plate matings and subsequent PCR analysis of transconjugants confirmed that vanB2 and Tn5382-like sequences were
transferred from each of 3 E. faecium and 1 E. faecalis donor isolates to both E. faecium GE-1 and
E. faecalis JH2-2 recipients (13). Cotransfer
of vancomycin and ampicillin resistance from the E. faecium
donors, which has been reported for isolates from the United States
(1, 6), was not detected for any of the transconjugants,
further confirming the lack of linkage of the vanB2 cluster
to pbp5.
VanB resistance among enterococci in the United Kingdom and the
Republic of Ireland is dominated by the vanB2 gene cluster and appears to have arisen by horizontal dissemination of the vanB2 gene cluster in association with a
Tn5382-type element.
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LETTER
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FOOTNOTES |
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* Phone: 44-1382-344270 E-mail: h.k.young{at}dundee.ac.uk
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Karen F. McGregor Carla Nolan Hilary-Kay Young* Department of Biological Sciences University of Dundee Dundee DD1 4HN United Kingdom | |||||
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Marie-France I. Palepou Luke Tysall Neil Woodford Antibiotic Resistance Monitoring and Reference Laboratory PHLS Central Public Health Laboratory Colindale, London NW9 5HT United Kingdom |
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