Transfer of the Virulence-Associated Protein A-Bearing Plasmid between Field Strains of Virulent and Avirulent Rhodococcus equi
Article first published online: 15 OCT 2013
Copyright © 2013 by the American College of Veterinary Internal Medicine
Journal of Veterinary Internal Medicine
Volume 27, Issue 6, pages 1555–1562, November/December 2013
How to Cite
Stoughton, W., Poole, T., Kuskie, K., Liu, M., Bishop, K., Morrissey, A., Takai, S. and Cohen, N. (2013), Transfer of the Virulence-Associated Protein A-Bearing Plasmid between Field Strains of Virulent and Avirulent Rhodococcus equi. Journal of Veterinary Internal Medicine, 27: 1555–1562. doi: 10.1111/jvim.12210
- Issue published online: 13 NOV 2013
- Article first published online: 15 OCT 2013
- Manuscript Accepted: 27 AUG 2013
- Manuscript Revised: 7 AUG 2013
- Manuscript Received: 2 JUL 2013
- Link Equine Research Endowment
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.
To estimate the frequency of transfer of the virulence plasmid between virulent and avirulent strains of R. equi derived from foals and their environment.
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.
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 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.