Equine Methicillin-Resistant Sequence Type 398 Staphylococcus aureus (MRSA) Harbor Mobile Genetic Elements Promoting...

Area of Science:

• Veterinary Microbiology
• Zoonotic Diseases
• Antimicrobial Resistance

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a biosafety risk in equine clinics.
• The emergence of multi-drug resistant zoonotic pathogens necessitates understanding their transmission and adaptation.

Purpose of the Study:

• To investigate the occurrence of MRSA in equine patients.
• To characterize mobile genetic elements and virulence factors in MRSA isolates.
• To assess the potential for MRSA adaptation and spread across host species.

Main Methods:

• Hygiene screening of equine patients for MRSA carriage.
• Antimicrobial susceptibility testing.
• Whole-genome sequencing and genomic composition analysis.
• Detection of virulence factors, mobile genetic elements, and toxins.

Main Results:

• 3.5% of equine patients carried MRSA, belonging to sequence type (ST) 398_t011.
• MRSA isolates exhibited additional antimicrobial resistances and harbored Staphylococcal Pathogenicity Island (SaPIbov5).
• A significant proportion carried a ΦSa3 phage encoding the human-specific Immune Evasion Cluster (IEC), and a rare equid-specific leukotoxin phage (Saeq1).

Conclusions:

• MRSA-ST398 in horses harbors diverse mobile genetic elements and immune evasion factors.
• These genetic combinations likely contribute to MRSA's adaptation and epidemic spread across different hosts.
• MRSA-ST398 may exhibit a host "generalist" phenotype, increasing zoonotic potential.