Phylogenetic analysis of Staphylococcus aureus CC398 reveals a sub-lineage epidemiologically associated with infections in horses.
Authors: Abdelbary Mohamed M H, Wittenberg Anne, Cuny Christiane, Layer Franziska, Kurt Kevin, Wieler Lothar H, Walther Birgit, Skov Robert, Larsen Jesper, Hasman Henrik, Fitzgerald J Ross, Smith Tara C, Wagenaar J A, Pantosti Annalisa, Hallin Marie, Struelens Marc J, Edwards Giles, Böse R, Nübel Ulrich, Witte Wolfgang
Journal: PloS one
Summary
# Editorial Summary CC398 is a methicillin-resistant *Staphylococcus aureus* (MRSA) clonal complex that emerged in pig farming but has since spread across multiple animal species; this multinational research team sequenced 97 housekeeping genes across 195 CC398 isolates to map the evolutionary relationships and epidemiological patterns within this lineage. Through phylogenetic analysis, they identified a distinct sub-clade (dubbed 'clade C') that has become strongly associated with equine nosocomial infections, spreading within and between horse hospitals whilst colonising veterinary staff (the association was statistically significant at p = 2 × 10⁻⁷). Notably, whilst clade C dominated *S. aureus* isolates from horses in veterinary-care settings, it remained exceptionally rare in human clinical infections, suggesting a preferential adaptation to equine hosts or hospital environments rather than human pathogenesis. For equine practitioners, this finding indicates that CC398 MRSA infections in horses may represent a distinct epidemiological problem centred on veterinary facilities, with potential for staff-mediated transmission between animals and premises—emphasising the importance of biosecurity protocols and staff hygiene in preventing nosocomial spread. Understanding this horse-specific sub-lineage may inform infection-control strategies and help distinguish equine-associated CC398 strains from broader zoonotic transmission risks.
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Practical Takeaways
- •Equine veterinarians and hospital staff should be aware that a specific CC398 sub-clone circulates in equine hospitals and can colonise personnel—infection control measures targeting this lineage may reduce nosocomial transmission
- •S. aureus CC398 from horses shows different epidemiological patterns than the pig-associated strains; equine-specific infection control protocols should be considered
- •Personnel working in equine hospitals may carry this equine-associated strain and could contribute to its spread between facilities
Key Findings
- •A specific CC398 sub-clone (clade C) is strongly associated with equine S. aureus infections in veterinary-care settings (p = 2 × 10⁻⁷)
- •Clade C spreads within and between equine hospitals causing nosocomial infections in horses and colonising veterinary staff
- •Clade C remains extremely rare among human S. aureus infections despite being common in equine settings
- •CC398 phylogenetic analysis identified 96 bi-allelic polymorphisms across 97 housekeeping loci in 195 isolates from multiple countries and host species