JAC Advance Access published online on September 30, 2003
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkg445
© 2003 by The British Society for Antimicrobial Chemotherapy
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Original article
1 Department of Microbiology
and Biomedical Sciences, Università Politecnica delle Marche,
Via Ranieri,
Monte d'Ago, 60131 Ancona;
* Corresponding author. E-mail: f.biavasco{at}unian.it.
Received 19 May 2003
; revised 9 August 2003
; accepted 15 August 2003
Objectives: Four Enterococcus
gallinarum isolates, all highly resistant to vancomycin, were
studied in order to investigate their relationship and to gain insight
into the molecular events responsible for their acquired resistance. Methods: Extensive molecular analysis was performed
to compare the four E. gallinarum isolates and
their Tn1546-like elements. Results: The four strains had very similar random
amplified polymorphic DNA (RAPD) patterns and different but related
PFGE profiles. Genotypic analysis demonstrated that all carried
both vanC-1 and vanA genes. Using
a vanA probe, no hybridization was detected to
plasmid DNA, whereas hybridization to different SmaI fragments
of the four strains was obtained with total DNA. Amplification and
sequencing experiments showed that all four strains carried a Tn1546-like element that contained the orf2, vanR, vanS, vanH, vanA and vanX genes and was flanked
at both ends by oppositely oriented IS1216V sequences.
On the left side of the vanA cluster, all lacked
IRL, and all had, upstream from orf2,
1029 bp of the 3' end of orf1.
On the right side, one of the strains lacked vanY, vanZ and IRR, whereas in one of the
other three there was an IS1542 element inserted
within the vanZ gene. In one strain, an additional
IS1216V element was inserted in the intergenic region vanX-vanY. Conclusions: This is the first study providing
a molecular analysis of chromosomal Tn1546-like
elements (possibly composite transposons) associated with high-level
vancomycin resistance in human and animal strains of E.
gallinarum. These molecular findings, together with those from
PFGE and RAPD, suggest that the four E. gallinarum isolates
are related and might have a common ancestor.
Keywords: glycopeptide-resistant enterococci, human and
animal enterococci, VanA phenotype
Molecular analysis of Tn1546-like
elements mediating high-level vancomycin resistance in Enterococcus
gallinarum
2 Laboratory of Bacteriology and Medical Mycology,
Istituto Superiore di
Sanità, 00161 Rome, Italy
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