Characterization of a fourth streptococcal pyrogenic exotoxin (SPE D)

A fourth streptococcal pyrogenic exotoxin (SPE D) was isolated from a pathogenic strain of group A streptococci cultured from a patient with a fatal case of streptococcal fasciitis associated with hypocalcemia and ‘toxic’ syndrome. SPE D was partially purified by differential solubility in ethanol and acetate-buffered saline and thin-layer isoelectric focusing. SPE D was antigenically distinct from the other streptococcal exotoxins SPE A, SPE B and SPE C. The isoelectric point of this exotoxin (4.6) was lower than those of the other SPEs. The Mr was estimated to be 13 000, and the biological activities were similar to the other exotoxins. SPE D reacted synergistically with SPE C (also present in this strain of streptococcus) to enhance the lethal effect of endotoxin in rabbits. The role of SPEs in the pathogenicity of this organism is discussed.