Identification and characterization of novel Staphylococcus aureus pathogenicity islands encoding staphylococcal...

Horizontal transfer of Staphylococcus aureus pathogenicity islands (SaPIs) plays an important role in acquiring pathogenicity. This study aimed to identify novel SaPIs encoding staphylococcal enterotoxins (SEs) and to characterize their SE productivity and replication process.

Four novel SaPIs (SaPITokyo12413, SaPITokyo11212, SaPITokyo12571 and SaPITokyo12381) were determined using the SaPI scanning method. These SaPIs were composed of mosaic structures containing reported sequences. Four strains harbouring novel SaPIs produced significant amounts of SEs to cause staphylococcal food poisoning (SFP). With focus on the interaction between the replication initiator protein (Rep) and the replication origin (ori sites) that are proposed to be important for the replication of SaPIs, each Rep was prepared and their two functions were confirmed: binding activity to ori sites and helicase activity. These activities were present in the Reps of SaPITokyo11212, SaPITokyo12571 and SaPITokyo12381, but were both absent in the Rep of SaPITokyo12413.

All four novel SaPIs could give sufficient toxicity to Staph. aureus to cause SFP. However, SaPITokyo12413 may be restricted in its replication capacity, suggesting that it lacks transfer ability unlike the other SaPIs.

This is the first report to identify four novel SE-encoding SaPIs and to examine their toxicity and replication capacity. Because SaPIs deeply participate in SE acquisition, it is important to elucidate their characteristics for understanding Staph. aureus virulence and speculating regarding its evolution as a pathogen.