Mitogenic factors from group G streptococci associated with scarlet fever and streptococcal toxic shock syndrome

Abstract

Since 1987, over 30 group G streptococcus (GGS) clinical isolates have been referred our laboratory and 3 have been investigated for production of streptococcal pyrogenic exotoxins(SPEs) A, B, and C. One isolate was associated with scarlet fever and two others with streptococcal toxic shock syndromes(STSS). All three isolates were grown in culture and shown not to produce SPEs A, B, and C by double immunodiffusion and Western blotting of ethanol precipitated, concentrated culture fluid. Isolated DNA from these organisms, separated by agarose gel electrophoresis, blotted on nylon membranes and developed with a digoxigenin detection system, failed to hybridize with probes specific for the genes speA, speB, and speC. We next investigated these isolates for the production of antigenically distinct mitogens by subjecting ammonium sulfate or ethanol precipitated culture fluids to isoelectric focusing(IEF) and assaying fractions from IEF for mitogenicity by use of a rabbit splenocyte proliferation assay. All three isolates showed three peaks of mitogenic activity. The two largest peaks of mitogenic activity from one isolate were assayed for pyrogenicity and the ability to enhance lethal lipopolysaccharide (LPS) shock in a rabbit model. After injection of the sample, rabbits were observed for 4 hours and then given a sub-lethal injections of LPS. All the rabbits exhibited fever but none died. In an earlier experiment, all rabbits exhibited fever and 2/3 died. These results indicate that GGS produce mitogenic factors which are distinct from SPEs A, B, and C and could be novel superantigens.