The whole genome of Staphylococcus aureus MW2, a pathogen causing community-acquired infections, was sequenced and compared with that of the hospital-acquired S. aureus N315 and others to unveil the high toxicity of MW2 infection. Differences in the genomic sequences of N315 and MW2 amount to about 5% and the presence of seven 'genomic islands' was noticed. A new type of island termed 'cassette chromosome' was also recognized in MW2 that leads to the penicillin/cefem-resistance by inserting into the MW2 chromosome. In addition, MW2 was newly found to possess 19 putative virulence factors which may be active and, when brought together, may cause a strong virulence.

This bacterium is one of the major pathogens causing community-acquired infections. In the Midwestern US, several fatal infections caused by MW2 were reported in late 90's. Combination of the distinct allelic forms of genomic islands found in different strains of S. aureus appears to be the genetic basis in determining the pathogenicity of medically important S. aureus strains including MW2. This information may be important for the detection of S. aureus infections in future.