Many bacteria belonging to the genus Staphylococcus are pathogenic to human, of which S. aureus is the most virulent. Other staphylococcal species are less virulent, but they also cause hospital infections especially in immuno-compromised patients. S. haemolyticus is known to colonize on the skin of virtually all human individuals and can be commonly isolated from axillae, perineum, and inguinal areas and is notorious for its multi-drug resistance. Indeed, it was this bacterium that was reported to have acquired resistance to methicillin and glycopeptide antibiotics such as Teicoplanin and Vancomycin in historically early stages. Also, S. haemolyticus can frequently be isolated from human blood cultures and is suspected to cause septicemia, peritonitis, otitis, and urinary tract infections.

To elucidate the mechanism responsible for the apparent genetic plasticity of the genome of S. haemolyticus that might result in its multi-drug-resistance phenotype and to understand its evolutionary relationship with other staphylococcal species, in particular the two S. aureus species whose genomes were previously analyzed at NITE, whole genome sequencing of S. haemolyticus strain JCSC1435 was initiated. The genome is 2.69 Mb in size with the G+C content of 32.8 % and shows about 40 % overall similarity to the genomes of S. aureus species. It contains three small plasmids. One of the most striking features of the genome of this bacterium is its richness in repeat sequences including a large number and variety of insertion sequences (IS's) as well as other types of repeats. The length of these repeats totals as much as some 5 % of the genome. It is suspected that some of the IS's thus identified might have been involved in the transfer of antibiotic resistance to other related staphylococcal species.