JAC Advance Access originally published online on March 9, 2007
Journal of Antimicrobial Chemotherapy 2007 59(5):1005-1009; doi:10.1093/jac/dkm057
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Co-transfer of vanA and aggregation substance genes from Enterococcus faecalis isolates in intra- and interspecies matings
1 Institute of Microbiology and Biomedical Sciences, Polytechnic University of Marche, 60100 Ancona, Italy 2 Department of Technologies and Health, Istituto Superiore di Sanità, 00161 Rome, Italy 3 Department of Biology, University of Genova, 16132 Genova, Italy
Received 17 October 2006; returned 21 November 2006; revised 23 January 2007; accepted 31 January 2007
* Corresponding author. Tel: +39-071-2206-296; Fax: +39-071-2206-293; E-mail: b.facinelli{at}univpm.it
Objectives: The study was undertaken to investigate vancomycin-resistant (vanA) Enterococcus faecalis isolates carrying aggregation substance (AS) gene(s) for their ability to co-transfer vanA and AS genes.
Methods: Six vanA clumping-positive E. faecalis isolates (five human and one food sample) carrying one or more AS genes (prgB, asa1, asa373) were analysed for co-transfer of vanA and AS genes to E. faecalis JH2-2 and Enterococcus faecium 64/3.
Results: E. faecalis isolates harboured one or multiple plasmids carrying vanA, one or more AS gene(s) or both. vanA was transferred to JH2-2 (frequencies of 10–3–10–6) from all donors and to 64/3 (10– 6–10– 8) only from donors from humans. AS genes were detected in 51/60 (85%) of JH2-2 and in 20/50 (40%) of 64/3 vanA transconjugants (prgB, asa1, asa373 or prgB asa373), of which a total of 53.6% were clumping-positive. The plasmid content of JH2-2 transconjugants from the same donor was either identical to that of the donor or it was completely different, suggesting different mechanisms for co-transfer (location on the same pheromone plasmid, mobilization of vanA plasmids by the pheromone-inducible conjugation system, rearrangement of plasmid content during matings). After induction with pheromones, a marked increase in adhesion to Caco-2 cells was observed in four isolates and in some JH2-2 transconjugants, all clumping-positive.
Conclusions: Findings suggest that co-transfer of vanA and AS genes may be a common feature of E. faecalis isolates. Since AS is recognized as a virulence factor, this feature might contribute to the emergence of strains with enhanced ability to cause infection and disease in humans.
Keywords: E. faecalis , prgB , asa1 , asa373