Virulence strategies of the dominant USA 300 lineage of community‐associated methicillin‐resistant S taphylococcus aureus ( CA ‐ MRSA )

Methicillin‐resistant S taphylococcus aureus ( MRSA ) poses a serious threat to worldwide health. Historically, MRSA clones have strictly been associated with hospital settings, and most hospital‐associated MRSA ( HA ‐ MRSA ) disease resulted from a limited number of virulent clones. Recently, MRSA has spread into the community causing disease in otherwise healthy people with no discernible contact with healthcare environments. These community‐associated MRSA clones ( CA ‐ MRSA ) are phylogenetically distinct from traditional HA ‐ MRSA clones, and CA ‐ MRSA strains seem to exhibit hypervirulence and more efficient host : host transmission. Consequently, CA ‐ MRSA clones belonging to the USA 300 lineage have become dominant sources of MRSA infections in N orth A merica. The rise of this successful USA 300 lineage represents an important step in the evolution of emerging pathogens and a great deal of effort has been exerted to understand how these clones evolved. Here, we review much of the recent literature aimed at illuminating the source of USA 300 success and broadly categorize these findings into three main categories: newly acquired virulence genes, altered expression of common virulence determinants and alterations in protein sequence that increase fitness. We argue that none of these evolutionary events alone account for the success of USA 300, but rather their combination may be responsible for the rise and spread of CA ‐ MRSA .