Characterization and distribution of a new enterotoxin-related superantigen produced by Staphylococcus aureus

Staphylococcal enterotoxins (SEs) are a family of structurally related pyro genic exotoxins consisting of the five prototypic SEs (types A to E) and th ree newly characterized SEs (types G to I) produced by Staphylococcus aureu s (S. aureus). They also work as superantigens and cause food poisoning and shock symptoms in humans. In this study, we cloned a new variant gene of t he seg and characterized its superantigenic properties and distribution amo ng the clinical isolates of S. aureus. The gene encodes a 233 amino acid pr otein which is highly homologous to SEG (97.7%), The variant SEG (SEGv) exp ressed by the cloned gene exerted mitogenic activity on human peripheral bl ood mononuclear cells at the concentration of 100 pg/ml T cells bearing V b eta 3, 12, 13.1, 13.2, 14 and 15 were preferentially expanded after stimula tion with the recombinant protein. The mRNA of the variant seg gene was det ected in the total RNA of the organisms bearing this gene. By PCR, 27 out o f 48 clinical isolates of S, aureus (56%) possessed either the seg or varia nt seg gene. These findings suggest that SEG, or SEGv, is one of the most f requently produced superantigen exotoxins by S, aureus and may participate in the inflammatory process of the host by activating a distinct set of V b eta families of T cells.