Transfer of the virulence-associated protein a-bearing plasmid between field strains of virulent and avirulent Rhodococcus equi.
Authors: Stoughton W, Poole T, Kuskie K, Liu M, Bishop K, Morrissey A, Takai S, Cohen N
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: *Rhodococcus equi* Plasmid Transfer in Field Strains Rhodococcus equi remains a significant cause of pneumonia and abscessation in foals, with virulence primarily determined by the presence of a virulence-associated protein (VAP)-encoding plasmid; however, little was known about whether this plasmid could transfer between virulent and avirulent field strains co-existing in the foal's environment and faeces. Stoughton and colleagues investigated plasmid transfer capacity by exposing avirulent R. equi isolates to virulent field strains under laboratory conditions that simulated aspects of the equine gastrointestinal tract. The researchers demonstrated that plasmid transfer between field strains does occur, with avirulent isolates acquiring the VAP-bearing plasmid and subsequently expressing virulent phenotypes. These findings have important epidemiological implications: the presence of both virulent and avirulent R. equi in the environment means that even initially avirulent isolates represent a potential threat if plasmid transfer occurs, complicating efforts to control foal infections through simple strain identification alone. For equine professionals managing R. equi in breeding operations, this research underscores the importance of comprehensive biosecurity measures and environmental management strategies rather than relying solely on bacterial strain typing to predict infection risk.
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Practical Takeaways
- •R. equi foal infections involve complex plasmid transfer between strains in the environment, meaning infection sources may be more dynamic than previously thought
- •Both virulent and avirulent R. equi are present in normal horse feces and pasture environments, so complete elimination from facilities is likely impossible
- •Knowing plasmid transfer occurs between strains may inform biosecurity and management strategies to reduce foal exposure to virulent isolates
Key Findings
- •Virulent and avirulent R. equi isolates coexist in equine feces and environmental sources affecting foals
- •Plasmid transfer between field strains of R. equi occurs, though the extent remains poorly characterized
- •Understanding plasmid transfer patterns is critical for epidemiology of R. equi foal infections