title: Secondary transfer and expression of vanA in Enterococcus faecium derived from a commensal vancomycin-susceptible Enterococcus faecium multi-component food isolate.
abstract: We investigated the potential for vancomycin-susceptible Enterococcus (VSE) from multi-component salads to disseminate vanA from four clinical vancomycin-resistant enterococci to 14 streptogramin-resistant enterococci (SRE) of food and animal origin. Strains were selected from a previous study based on the presence of streptogramin susceptibility and/or vanA, vanB, vatD, vatE, agg, cpd, and gelE genes. Transconjugants were isolated on brain heart infusion agar containing vancomycin and selective antibiotics. Thirty-nine matings using a 1:10 donor-recipient ratio for filter and broth methods resulted in transfer of vanA between an agg(+)cpd(+)gelE(+) Enterococcus faecalis donor and an agg(-)cpd(-)gelE(-) streptogramin-susceptible Enterococcus faecium salad recipient at a frequency of 10(-8) per recipient by filter method. Secondary mating of the transconjugant with SR/VSE strains resulted in a two- to four-log-fold greater frequency of transfer. Reverse transcription-polymerase chain reaction revealed vanA RNA products in the transconjugant cultivated in nutrient broth and salad at 37°C in the presence and absence of recipient filtrate. This study demonstrated that native salad VSE disseminated vanA to SRE carrying agg, cpd, and/or gelE. An increase in transfer efficiency resulted from secondary conjugation using the native vancomycin- and streptogramin-susceptible salad strain as the donor.
authors.affiliation: Department of Food Science, Rutgers University, New Brunswick, New Jersey, USA.
authors.forename: Erin A
authors.initials: EA
authors.lastname: Christensen
authors.forename: Kim
authors.initials: K
authors.lastname: Joho
authors.forename: Karl R
authors.initials: KR
authors.lastname: Matthews
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D019729:Carbon-Oxygen Ligases / Q000096:biosynthesis / Q000235:genetics*; D002417:Cattle; D003227:Conjugation, Genetic; D016984:Enterococcus faecium / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics* / Q000302:isolation & purification; D005516:Food Microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D025361:Streptogramins / Q000494:pharmacology; D014640:Vancomycin / Q000494:pharmacology; D020713:Vancomycin Resistance / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D025361:Streptogramins; C071437:VanA ligase, Bacteria; D014640:Vancomycin; D019729:Carbon-Oxygen Ligases