Comparative genotypic and phenotypic characterisation of methicillin-resistant Staphylococcus aureus ST398 isolated from animals and humans.
Authors: Jamrozy Dorota M, Fielder Mark D, Butaye Patrick, Coldham Nick G
Journal: PloS one
Summary
# Editorial Summary: MRSA ST398 Genetic Characteristics in Equine and Other Animal Species MRSA ST398 has become predominant in pig populations across Europe and North America, with documented spillover to other animal species including horses, yet the genetic basis for this lineage's success remained unclear. Researchers compared virulence and antimicrobial resistance gene profiles across 18 ST398 isolates and 48 isolates from seven other sequence types using DNA microarray and PCR, examining both animal and human sources. ST398 strains were notable for carrying the lowest content of virulence genes among all lineages tested, lacking the accessory virulence factors present in other MRSA types, yet paradoxically demonstrated significant diversity and high carriage of antimicrobial resistance determinants—comparable to equine-associated MRSA ST8. Whilst the genetic profile suggests ST398 relies on a minimalist virulence strategy rather than enhanced pathogenic mechanisms, the high prevalence of resistance genes indicates that survival and transmission advantages stem primarily from antibiotic resistance rather than enhanced virulence potential. For equine practitioners, this suggests that whilst ST398 may not represent a hypervirulent threat, the strain's robust antimicrobial resistance profile warrants judicious antibiotic stewardship and enhanced infection control protocols, particularly given the documented zoonotic potential.
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Practical Takeaways
- •MRSA ST398's success in animal populations appears driven by antimicrobial resistance rather than enhanced virulence, suggesting control strategies should focus on limiting antibiotic exposure
- •Equine practitioners should be aware that equine-associated MRSA ST8 shares similar high antimicrobial resistance profiles to the zoonotic ST398 strain, with implications for treatment planning
- •The lack of specific virulence markers in ST398 does not indicate lower clinical risk; focus infection control protocols on the strain's documented prevalence in swine and other animals rather than assuming reduced pathogenicity
Key Findings
- •MRSA ST398 displayed the lowest content of virulence genes compared to other sequence types (ST5, ST8, ST15, ST22, CC30, CC97, CC130, CC151)
- •ST398 isolates lacked accessory virulence genes present in other lineages but maintained high diversity in antimicrobial resistance gene profiles
- •Antimicrobial resistance gene profiles varied significantly within the same sequence type, with ST398 showing comparable resistance gene content to equine MRSA ST8
- •No ST398-specific virulence markers could be identified despite the lineage's epidemiological success across multiple animal species