Transfer of the virulence-associated protein a-bearing plasmid between field strains of virulent and avirulent Rhodococcus equi. Academic Article uri icon


  • 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. OBJECTIVES: To estimate the frequency of transfer of the virulence plasmid between virulent and avirulent strains of R. equi derived from foals and their environment. ANIMALS: 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, 0.030.43%). 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 AND CLINICAL IMPORTANCE: Transfer of the virulence plasmid occurs with relatively high frequency. These findings could impact strategies to control or prevent R. equi through environmental management.

published proceedings

  • J Vet Intern Med

author list (cited authors)

  • Stoughton, W., Poole, T., Kuskie, K., Liu, M., Bishop, K., Morrissey, A., Takai, S., & Cohen, N.

citation count

  • 3

complete list of authors

  • Stoughton, W||Poole, T||Kuskie, K||Liu, M||Bishop, K||Morrissey, A||Takai, S||Cohen, N

publication date

  • November 2013