The article provides a comprehensive analysis of the evolutionary history and nomenclature of methicillin-resistant Staphylococcus aureus (MRSA). Using multilocus sequence typing (MLST) and the burst algorithm, the authors identified 11 major MRSA clones within five groups of related genotypes. They resolved the evolutionary origins of these clones, establishing that MRSA has repeatedly emerged from successful epidemic methicillin-susceptible S. aureus (MSSA) strains. The study also highlighted the horizontal transfer of the methicillin resistance gene (mecA) and the increasing drug resistance within a small number of ecologically successful S. aureus genotypes. The authors proposed a rational nomenclature for MRSA clones, defining them by both their genotype (ST) and their SCCmec type. The findings suggest that MRSA evolution is driven by the horizontal transfer of the mec determinant into different lineages, rather than diversification from a single original clone.The article provides a comprehensive analysis of the evolutionary history and nomenclature of methicillin-resistant Staphylococcus aureus (MRSA). Using multilocus sequence typing (MLST) and the burst algorithm, the authors identified 11 major MRSA clones within five groups of related genotypes. They resolved the evolutionary origins of these clones, establishing that MRSA has repeatedly emerged from successful epidemic methicillin-susceptible S. aureus (MSSA) strains. The study also highlighted the horizontal transfer of the methicillin resistance gene (mecA) and the increasing drug resistance within a small number of ecologically successful S. aureus genotypes. The authors proposed a rational nomenclature for MRSA clones, defining them by both their genotype (ST) and their SCCmec type. The findings suggest that MRSA evolution is driven by the horizontal transfer of the mec determinant into different lineages, rather than diversification from a single original clone.