Isolation of VanB-Type Enterococcus faecalis Strains from Nosocomial Infections: First Report of the Isolation and Identification of the Pheromone-Responsive Plasmids pMG2200, Encoding VanB-Type Vancomycin Resistance and a Bac41-Type Bacteriocin, and pMG2201, Encoding Erythromycin Resistance and Cytolysin (Hly/Bac)

Abstract

Eighteen identical VanB-type Enterococcus faecalis isolates that were obtained from different hospitalized patients were examined for their drug resistance and plasmid DNAs. Of the 18 strains, 12 strains exhibited resistance to erythromycin (Em), gentamicin (Gm), kanamycin (Km), tetracycline (Tc), and vancomycin (Van) and produced cytolysin (Hly/Bac) and a bacteriocin (Bac) active against E. faecalis strains. Another six of the strains exhibited resistance to Gm, Km, Tc, and Van and produced a bacteriocin. Em and Van resistance was 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 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 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 plasmid pCF10. pMG2200 also encoded TraE1, a key positive regulator of plasmid pAD1, indicating that pMG2200 is a naturally occurring chimeric plasmid that has a resulting prgX-prgQ-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 pheromoneindependent plasmid pHT␤ 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.

Current Trends of Emergence and Spread of Vancomycin-Resistant Enterococci

“…In contrast, vanB-type elements preferably integrate into the chromosome, but are mobile as part of integrative and conjugative elements ICE (Paulsen et al, 2003;Hegstad et al, 2010). Occasionally vanB resides on (transferable) plasmids Zheng et al, 2009); as noticed recently associated with larger VanB-type VRE outbreaks (Sivertsen et al, 2011;Bjorkeng et al, 2011). Many surveillance studies failed to recognize a considerable reservoir of vanB among enterococcal colonizers in animals and humans, whereas recent real-time based studies targeting vanB or improved methods of detection revealed a considerable reservoir among intestinal colonizers, maybe also non-enterococcal bacteria (see above).…”

“…vanB could be subdivided into three different allele types (vanB1-3) with vanB-2 the most prevalent type worldwide. The vanB alleles are part of Tn1547 or the conjugative transposon Tn1549/5382 which are mainly chromosomally located and less frequently, on plasmids (Werner et al, 2006;Zheng et al, 2009;Hegstad et al, 2010;Bjorkeng et al, 2011). The main clinical relevant reservoir of vanA and vanB elements is in E. faecium, at least in Europe, Northern and Latin America and Southeast Asia, although they have also been observed occasionally in other enterococcal species (see Table 1 and below) (Zirakzadeh and Patel 2005;Werner et al, 2008a;Werner 2011).…”

vanA in vancomycin-resistant Enterococcus faecalis isolated in Baghdad

“…Our results detected that all vancomycin resistant E. faecalis isolates were resistant to Oxacillin, Cefepime, Rifampicin and Tetracycline. Multiple-drug-resistant enterococci and vancomycinresistant enterococci (VRE), in particular, are opportunistic pathogens and major causes of nosocomial infections in immunocompromised patients (Zheng et al, 2009).…”

ICE Slu van, a 94-Kilobase Mosaic Integrative Conjugative Element Conferring Interspecies Transfer of VanB-Type Glycopeptide Resistance, a Novel Bacitracin Resistance Locus, and a Toxin-Antitoxin Stabilization System

“…As an integral part of the conjugative transposon Tn5382/Tn1549, vanB2 is the most-widespread subtype in clinically important enterococci (30,33,34,35,36,37,38). Tn5382/ Tn1549 is able to support transfer of the vanB2 operon from Clos-tridium to enterococci in the intestinal environment (39), but the transposon is more often transferred as a part of larger chromosomal elements or plasmids (30,35,37,40,41).…”