Uniform TitleHorizontal transfer of vanA-mediated resistance among commensal and streptogramin-resistant enterococci derived from multi-component food systems
NameChristensen, Erin A. (author), Matthews, Karl (chair), Montville, Thomas (internal member), Tchikindas, Mikhail (internal member), White, David (outside member), Rutgers University, Graduate School - New Brunswick,
DescriptionThe enterococci are commensal lactic acid bacteria of the gastrointestinal tract of humans and animals, and are ubiquitous in nature. They have a long history of use as starter cultures in European fermented foods and are used commercially as probiotics. Within the past two decades, vancomycin-resistant enterococci (VRE) have emerged as significant nosocomial pathogens, treatable with few antibiotics. In the US, the agricultural use of virginiamycin, a streptogramin growth promoter, has raised concern regarding cross-resistance among VRE to the clinical streptogramin quinupristin-dalfopristin. Horizontal transfer of antibiotic resistance genes is mediated by aggregation substances and sex pheromones that induce conjugation, but the role of these virulence factors in enterococci of food origin is largely unknown. The potential for enterococci isolated from multi-component creamy deli salads (including macaroni, potato, chicken, and seafood) to harbor and disseminate the high-level vancomycin resistance gene vanA among more virulent native enterococci was investigated. Initial filter mating between a clinical Enterococcus faecalis isolate carrying vanA and a commensal, vancomycin susceptible E. faecium salad recipient that harbored no virulence genes was demonstrated at a frequency of 10-8 per recipient. The rate of secondary transfer of vanA by this transconjugant to both food and animal enterococci carrying the streptogramin resistance genes vatE or vatD and/or the selected virulence genes agg, gelE, cpd, and efa increased three log-fold. In primary and secondary matings, multiple antibiotic resistance patterns increased for all transconjugants. Additionally, expression of vanA in the absence of selective antibiotic pressure was determined by reverse transcriptase-PCR and found to occur in the primary transconjugant but not in the donor. Results demonstrate that foodborne commensal enterococci from multi-component foods can receive and disseminate vanA to food and animal enterococci that harbor streptogramin resistance and/or virulence genes. The potential for transfer events to occur among commensal and virulent enterococci in foods must be considered for the safe use of Enterococcus in starter cultures and probiotics.
NoteIncludes bibliographical references.
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.