Plasmid Profiles of Virulent Rhodococcus equi Strains Isolated from Infected Foals in Poland.
Authors: Kalinowski Marcin, Grądzki Zbigniew, Jarosz Łukasz, Kato Kiyoko, Hieda Yu, Kakuda Tsutomu, Takai Shinji
Journal: PloS one
Summary
# Editorial Summary: Plasmid Profiles of Virulent *Rhodococcus equi* in Polish Foals *Rhodococcus equi* remains a significant cause of bronchopneumonia and abscessation in foals worldwide, with virulence dependent on expression of the 15–17 kDa VapA protein encoded on large plasmids of 85–90 kb; whilst 12 plasmid types have been identified in pathogenic strains globally, no data existed for Polish field isolates. Researchers characterised plasmid profiles from 10 clinical isolates recovered at necropsy from foals on 8 Polish farms and 11 environmental isolates from soil samples on 3 farms, using restriction fragment length polymorphism (RFLP) analysis with four endonucleases and comparison against 12 known reference strains. Among the 21 virulent isolates confirmed by PCR, all but one harboured the VapA 85 kb type I plasmid, with a single strain carrying the VapA 87 kb type I variant—demonstrating remarkable genetic uniformity across central and eastern Polish farms. This striking consistency suggests either a common source of infection and environmental contamination, or limited genetic diversity within the regional *R. equi* population, which has implications for epidemiological tracking, diagnostic strategy standardisation, and potentially for vaccine development targeting this particular plasmid type. For practitioners managing foals on Polish farms, these findings indicate that treatment protocols and management strategies addressing type I VapA strains should be particularly effective, though continued surveillance remains important given the disease's significant morbidity and mortality in young stock.
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Practical Takeaways
- •R. equi remains a significant threat to foals under 6 months old on Polish farms; farms should implement environmental sampling and biosecurity measures to reduce pasture contamination
- •The uniform plasmid profile in Polish strains suggests consistent virulence characteristics, which may inform diagnostic and treatment protocols, though resistance patterns should still be monitored
- •Environmental management (soil remediation, pasture rotation) may be effective control strategies given the environmental persistence of virulent strains identified in this study
Key Findings
- •All but one of 21 Polish R. equi isolates (clinical n=10, environmental n=11) harbored VapA 85 kb type I plasmid, indicating highly uniform plasmid pattern in Polish field strains
- •One isolate carried VapA 87 kb type I plasmid, representing first documented plasmid type variation in Polish R. equi strains
- •Virulent R. equi strains were confirmed by PCR detection of vapA gene and characterized by 15-17 kDa virulence-associated protein expression
- •Environmental soil samples from horse farms yielded virulent R. equi strains matching clinical isolates from diseased foals, suggesting farm environment as infection source