title: Transfer of the virulence-associated protein a-bearing plasmid between field strains of virulent and avirulent Rhodococcus equi.
abstract: BACKGROUND
  Virulent and avirulent isolates of Rhodococcus equi coexist in equine feces and the environment and are a source of infection for foals. The extent to which plasmid transfer occurs among field strains is ill-defined and this information is important for understanding the epidemiology of R. equi infections of foals.
  
  
  OBJECTIVE
  To estimate the frequency of transfer of the virulence plasmid between virulent and avirulent strains of R. equi derived from foals and their environment.
  
  
  METHODS
  None.
  
  
  METHODS
  In vitro study; 5 rifampin-susceptible, virulent R. equi isolates obtained from clinically affected foals or air samples from a farm with a history of recurrent R. equi foal pneumonia were each mixed with 5 rifampin-resistant, avirulent isolates derived from soil samples, using solid medium, at a ratio of 10 donor cells (virulent) per recipient cell. Presumed transconjugates were detected by plating on media with rifampin and colony immunoblotting to detect the presence of the virulence-associated protein A.
  
  
  RESULTS
  Three presumed transconjugates were detected among 2,037 recipient colonies, indicating an overall estimated transfer frequency of 0.15% (95% CI, 0.03–0.43%). All 3 transconjugates were associated with a single donor and 2 recipient strains. Genotyping and multiplex PCR of presumed transconjugates demonstrated transfer of the virulence-associated protein A-bearing plasmid between virulent and avirulent R. equi.
  
  
  CONCLUSIONS
  Transfer of the virulence plasmid occurs with relatively high frequency. These findings could impact strategies to control or prevent R. equi through environmental management.
authors.forename: W
authors.initials: W
authors.lastname: Stoughton
authors.forename: T
authors.initials: T
authors.lastname: Poole
authors.forename: K
authors.initials: K
authors.lastname: Kuskie
authors.forename: M
authors.initials: M
authors.lastname: Liu
authors.forename: K
authors.initials: K
authors.lastname: Bishop
authors.forename: A
authors.initials: A
authors.lastname: Morrissey
authors.forename: S
authors.initials: S
authors.lastname: Takai
authors.forename: N
authors.initials: N
authors.lastname: Cohen
mesh_terms: D000193:Actinomycetales Infections / Q000382:microbiology / Q000635:transmission / Q000662:veterinary*; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D003227:Conjugation, Genetic / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D006734:Horse Diseases / Q000382:microbiology* / Q000635:transmission; D006736:Horses; D015151:Immunoblotting / Q000662:veterinary; D066298:In Vitro Techniques; D010957:Plasmids / Q000235:genetics; D016929:Rhodococcus equi / Q000235:genetics / Q000472:pathogenicity*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; C541879:VapA protein, Rhodococcus equi