New SEB-encoding Staphylococcus aureus pathogenicity island

  • Katsuhiko Omoe, Department of Veterinary Medicine, Faculty of Agriculture, Iwate University, Japan
  • Dr Hideki Misu, Department of Veterinary Medicine, Faculty of Agriculture, Iwate University, Japan
  • Dr Megumi Saito, Department of Veterinary Medicine, Faculty of Agriculture, Iwate University, Japan
  • Dr Takeshi Nukui, Department of Veterinary Medicine, Faculty of Agriculture, Iwate University, Japan
  • Dong-Liang Hu, Department of Microbiology and Immunology, Hirosaki University Graduate School of Medicine, Japan
  • Dr Akio Nakane, Department of Microbiology and Immunology, Hirosaki University Graduate School of Medicine, Japan
  • Dr Kunihiro Shinagawa, Department of Veterinary Medicine, Faculty of Agriculture, Iwate University, Japan

    • Staphylococcal enterotoxins (SEs) are superantigens and emetic toxins, and are one of the major causes for food poisoning in humans. SEs have been divided into five serological types (SEA though to SEE). In the recent years, existence of many new types of SE or SEl (staphylococcal enterotoxin-like toxin), SEG to SElV, has been reported. These SE/SEl genes are carried by mobile genetic elements, such as prophage, pathogenicity islands (PI), and plasmids. In this study, we investigated diversity of SEB-encoding Staphylococcus aureus Pathogenicity island SaPI3-related PIs. It has been reported that SaPI3 carries seb, selk and selq. However, our previous study showed that there are several S. aureus strains that harbored seb without selk and selq. We designed LA-PCR primers corresponding to outside of SaPI3 insertion site on S. aureus genome to amplify entire SaPI3. SEB-positive S. aureus strains with several SE/SEl genotypes (2 strains per each genotype: type I seb; type II sea, seb, selk, selq; type III sea, seb, seh, selk, selq; type IV seb, seh; type V seb, selp; type VI seb, selk, selq; type VII seb, selk, selp, selq) were subjected to LA-PCR analysis. Approximately 15 Kbp of PCR products were observed in all strains with genotypes I, II, V, VI, VII, suggesting these strains are harboring SaPI3 or SaPI3-related sequences, whereas seb in genotype III and IV strains carried by non-SaPI3 mobile genetic element. Subsequently, we determined nucleotide sequences of the PCR product amplified from genotype I strain IVM-60 (SaPI-IVM60). SaPI-IVM60 is bordered by 17 bp direct repeats (ttattcctgctaaataa), as is the case of SaPI3. SaPI-IVM60 contains 16 open reading frames (orfs) including seb but not selk and selq, and 10 orfs including orf1 (int) showed high similarity to that of SaPI3. However, orf7 (rep) showed high similarity to rep gene of SaPI2, rather than SaPI3. These results suggest that recombination between SaPI2 and SaPI3 may have occurred, and such recombinational event may be important for evolution of SaPIs.