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Antimicrob. Agents Chemother. doi:10.1128/AAC.00754-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The Isolation of VanB-Type E. faecalis Strains From Nosocomial Infections: The First Report of Isolation and Identification of the Pheromone-Responsive Plasmids pMG2200 (106.5 kbp), Encoding VanB-Type Vancomycin Resistance and Bac41-Type Bacteriocin, and pMG2201 (65.7 kb), Encoding Erythromycin Resistance and Cytolysin (Hly/Bac)

Department of Bacteriology, and Laboratory of Bacterial Drug resistance, Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511; Japan and Institute of Clinical Pharmacology, Peking University First Hospital, Beijing 10034, China

^* To whom correspondence should be addressed. Email: tomitaha{at}med.gunma-u.ac.jp.

	Abstract

Eighteen identical VanB-type Enterococcus faecalis isolates that had been obtained from different hospitalized patients were examined for their drug resistances and plasmid DNAs. Of the 18 strains, thirteen strains exhibited resistance to erythromycin (Em), gentamicin (Gm), kanamycin (Km), tetracycline (Tc) and vancomycin (Van), and produced cytolysin (Cyt, (Hly/Bac)) and a bacteriocin (Bac) active against E. faecalis strains. Another five of the strains exhibited resistance to Gm, Km, Tc and Van, and produced a bacteriocin. The Em and Van resistances were transferred individually to E. faecalis FA2-2 strains at a frequency of about 10^-4 per donor cell by broth mating. The Em-resistant transconjugants and the Van-resistant transconjugants harbored a 65.7 kbp plasmid and a 106 kbp plasmid, respectively. The 106 kbp and 65.7 kbp plasmids isolated from the representative E. faecalis NKH15 strains were designated as pMG2200 and pMG2201, respectively. pMG2200 conferred vancomycin resistance and bacteriocin activity on the host strain and responded to the synthetic pheromone cCF10 for pCF10, while pMG2201 conferred erythromycin resistance and cytolysin activity on its host strain, and responded to the synthetic pheromone cAD1 for pAD1 The complete DNA sequence of pMG2200 (106,527 bp) showed that the plasmid carried a Tn1549-like element encoding vanB2-type resistance and the Bac41-like bacteriocin genes of the pheromone-responsive plasmid pYI14. The plasmid contained the regulatory region found in pheromone-responsive plasmids and encoded the genes PrgX and PrgQ, which are the key negative-regulatory elements for the pCF10 plasmid. pMG2200 also encoded TraE1, a key positive-regulator of the pAD1 plasmid, indicating that pMG2200 is a naturally-occurring chimeric plasmid that has a resulting perX-pergQ-traE1 genetic organization in the regulatory region of the pheromone response. The functional oriT region and the putative relaxase gene of pMG2200 were identified and found to differ from those of pCF10 and pAD1. The putative relaxase of pMG2200 was classified as a member of the MOB_MG family, which is found in the pheromone independent pHTplasmid of the pMG1-like plasmids. This is the first report of the isolation and characterization of a pheromone-responsive highly conjugative plasmid encoding vanB resistance.