Whole-genome sequencing and pathogenicity analysis of Rhodococcus equi isolated in horses.
Authors: Hu Bin, Gao Sichao, Zhang Hao, Li Qiaoqiao, Li Gaojian, Zhang Shuairan, Xing Yanan, Huang Yanyi, Han Shuyi, Tian Ying, Zhang Wei, He Hongxuan
Journal: BMC veterinary research
Summary
# Editorial Summary: Genomic and Pathogenicity Analysis of *Rhodococcus equi* Strain BJ13 *Rhodococcus equi* remains a significant threat to foal health, particularly in intensive breeding operations, yet our understanding of strain-specific virulence mechanisms remains incomplete. Researchers sequenced and characterised the complete genome of strain BJ13, isolated from a thoroughbred racehorse farm in Beijing, revealing a 5.30 Mb genome encoding 4,929 genes alongside a substantial virulence plasmid (0.08 Mb); critically, they identified 418 predicted virulence factors and 225 drug resistance genes distributed across mobile genetic elements including six gene islands and one integrated prophage. Experimental infection in mice demonstrated marked pathogenicity, with the strain triggering severe inflammatory lesions in pulmonary, hepatic and splenic tissues and achieving 50% mortality by day 7 post-infection—a response characterised by dysregulated immune signalling, including IL-10 overexpression alongside elevated pro-inflammatory cytokine production. These genomic findings, combined with the documented disease severity in animal models, suggest BJ13 represents a particularly aggressive strain that warrants investigation into whether its specific virulence gene profiles and drug resistance arsenal differ from historical isolates. For equine practitioners, this work underscores the importance of targeted antimicrobial stewardship in foal pneumonia cases and highlights the critical need for rapid diagnostic confirmation and susceptibility testing rather than empirical broad-spectrum therapy.
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Practical Takeaways
- •This R. equi strain shows significant virulence potential and multiple drug resistance genes—antimicrobial susceptibility testing should guide treatment selection in affected foals
- •The documented pathogenic mechanisms involving immune dysregulation highlight the need for supportive immunomodulatory care alongside antimicrobial therapy in R. equi cases
- •Genomic characterization of farm isolates can identify particularly virulent strains, informing biosecurity protocols on breeding farms
Key Findings
- •R. equi strain BJ13 genome contains 418 predicted virulence factors and 225 drug resistance genes that may enhance pathogenicity
- •The BJ13 strain caused inflammatory damage to lungs, liver, and spleen in mouse models with 50% mortality by day 7 post-infection
- •Pathogenicity involves complex immune dysregulation including IL-10 overexpression and elevated pro-inflammatory cytokines (TNF-α)
- •Genomic analysis identified 6 gene islands, 1 prophage, and a virulence plasmid structure contributing to evolutionary pathogenic potential