Identification and characterization of two novel superantigens among Staphylococcus aureus complex

Abstract Staphylococcal enterotoxins (SEs), also known as superantigens, play a very important role in infections and food poisoning caused by Staphylococcus aureus . Recently, S. argenteus and S. schweitzeri were recognized as novel species closely related to S. aureus . In this study of these three species, it was found that two putative SE genes were located upstream of some v Saβ pathogenicity islands and the deduced amino acid sequences showed l 26) and 27 (SE l 27), were identified and characterized among the three species. The mRNAs encoding SE l 26 and SE l 27 were expressed during all the growth phases. Recombinant SE l 26 and SE l 27 exhibited superantigenic activity in human peripheral blood mononuclear cells and mouse splenocytes by examining cell proliferation and cytokine production. Interestingly, these two genes were present universally in S. argenteus sequence type 2250 with clinical importance. Meanwhile, SE l 27 variants from different species showed differential sensitivity to human peripheral blood mononuclear cells, which corresponded to the primary bacterial species hosts. It was demonstrated from these results that SE l 26 and SE l 27 were characterized to be two novel SE toxins and some SEs evolved along with the bacteria when the organisms adapted the hosts’ immune systems.