Epidemiology of antibiotic resistance in Staphylococcus aureus.

The genetic equipment of Staphylococcus aureus is at least as comprehensive as other organisms. Transposons provide the potential for reassortment of genes between plasmids and the chromosome. At least six different mechanisms of gene transfer between cells are documented in vitro. Phage-mediated conjugation is the transfer mechanism most likely to occur between staphylococci in nature. MRSA have evolved from a single clone and are now heterogeneous in properties. Some may show decreased virulence. The origin of new resistant determinants is likely to be other human cultures of Staph. aureus rather than an animal staphylococcal reservoir.