Staphylococcus aureus is one of the major bacterial pathogens of man, causing a variety of diseases from mild skin and soft-tissue infections to severe invasive infections with high mortality. In the healthcare setting it is the most frequent cause of surgical site, lower respiratory tract and cardiovascular infections and the second most common cause of blood stream infections and pneumonia. The ability of S. aureus to develop resistance to all classes of antimicrobials, in particular the ß-lactams, has become a major global problem. In the pre-antibiotic era, the mortality rate for severe staphylococcal sepsis was as high as 90%. In a recent meta-analysis of nine studies of S. aureus bacteraemia in the antibiotic era, although the mean mortality rate due to methicillin-susceptible S. aureus (MSSA) was 12% (ranging from 0 to 38%), for methicillin-resistant S. aureus (MRSA) the mean was 29% (ranging from 8 to 50%). Whilst estimates vary, the mortality associated with MRSA is on average twice that with MSSA.