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Evaluation of Plasmid-transfer From Virulent to Avirulent Rhodococcus equi

Audrey Morrissey 1, Toni Poole 2, Jessica Nerren1, Noah Cohen 1

1 Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, TX, USA

2 Southern Plains Area Research Center, USDA-ARS, College Station, TX, USA

Structured Abstract

Objective – To determine the rate of transfer of the virulence-associated plasmid from virulent to avirulent Rhodococcus equi.

Animals or Sample Population – Laboratory strains of R. equi.

Procedure – A virulent isolate of R. equi susceptible to rifampicin (donor isolate) was grown together with an avirulent isolate of R. equi resistant to rifampicin (recipient isolate) in broth then streaked onto media plates.  Antibiotics were used in the media to selectively remove donor (virulent) isolates and leave only recipient bacteria and transconjugates on plates.  The efficiency of transfer was determined using quantitative microbiologic culture and a colony immunoblot assay.

Results – Results are pending: the study will document whether the plasmid is transferable by conjugation from a virulent isolate to an avirulent isolate, and the rate of transfer will be estimated

Conclusions and Clinical Relevance – Pending results: if the plasmid is transferable, results will indicate that virulent isolates from the feces of horses and in soil samples at farms are a repository for transfer of virulence to avirulent isolates which are ubiquitous in the environment of horses and foals.