Genomic characterisation of CC398 MRSA causing severe disease in Australia

Area of Science:

• Microbiology
• Genomics
• Epidemiology

Background:

• Clonal complex 398 (CC398) livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) is globally prevalent in food animals.
• Emergence of community-associated MRSA (CA-MRSA) variants, including Panton-Valentine leukocidin (PVL)-positive and negative clones, complicates CC398 epidemiology.

Purpose of the Study:

• To determine if ten recent CC398 MRSA bacteraemia cases in Australia originated from LA-MRSA or CA-MRSA CC398 strains.
• To investigate the genetic relatedness of Australian CC398 isolates to international clades.

Main Methods:

• Comparative genomic analysis of ten Australian CC398 MRSA bacteraemia isolates.
• Whole-genome sequencing (WGS) and phylogenetic comparison with global CC398 MRSA sequences.

Main Results:

• Australian CC398 isolates were phylogenetically linked to human-associated II-GOI and livestock-associated IIa clades.
• Identified CC398 MRSA clones included PVL-positive ST1232-V, PVL-negative CA-ST398-V, and LA-ST398-V.
• CC398 CA-MRSA appears established in the Australian community, and ST398-V LA-MRSA is widespread in piggeries.

Conclusions:

• WGS is essential for differentiating CC398 CA-MRSA from LA-MRSA and determining isolate origins.
• Findings highlight the establishment of CC398 CA-MRSA in Australia and the prevalence of ST398-V LA-MRSA in piggeries.
• Emphasizes the need for national One Health surveillance programs for antimicrobial resistance.