Molecular analysis of the chromosomal 16S rRNA gene and vapA plasmid gene of Polish field strains of R. equi.
Authors: Kalinowski Marcin, Grądzki Zbigniew, Jarosz Łukasz, Adaszek Łukasz
Journal: PloS one
Summary
Rhodococcus equi remains a significant threat to foals under six months of age, with virulence determined largely by the vapA plasmid gene, yet most research has focused on plasmid profiles rather than examining sequence variation in field strains. Polish researchers sequenced the 16S rRNA chromosomal gene and vapA plasmid gene fragments from 22 clinical isolates and 18 environmental samples collected from studs, comparing results against reference sequences in GenBank databases. The chromosomal 16S rRNA gene proved highly conserved across all Polish strains (99.5% similarity to reference sequences with no field variation), whilst vapA plasmid gene analysis revealed two distinct polymorphic variants with meaningful differences between clinical and environmental isolates. Environmental strains showed greater genetic variation, suggesting that exposure to adverse conditions on stud grounds creates selective pressure and drives DNA sequence changes in non-clinical populations. For practitioners, these findings highlight that whilst chromosomal markers offer limited diagnostic discrimination, vapA sequencing could distinguish between actively virulent clinical strains and the broader environmental reservoir, potentially refining infection risk assessment on contaminated premises and informing targeted management strategies during outbreak situations.
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Practical Takeaways
- •Environmental R. equi strains differ genetically from clinical strains isolated from infected foals, which may have implications for understanding transmission and virulence patterns on studs
- •The conservation of 16S rRNA sequences suggests this gene is not useful for differentiating R. equi strains; vapA gene analysis is more informative for strain characterization
- •Understanding the molecular differences between environmental and clinical R. equi strains could inform biosecurity and management strategies to reduce foal infection risk
Key Findings
- •16S rRNA gene sequences of Polish R. equi field strains were highly conserved with 99.5% similarity to reference sequences, showing no variation under field conditions
- •vapA plasmid gene analysis revealed two polymorphic variants with clear differences between clinical isolates from foals and environmental isolates from soil samples
- •Environmental R. equi strains showed greater DNA sequence variation than clinical strains, suggesting natural selection pressure from adverse external factors