Identification of a fourth staphylococcal enterotoxin, enterotoxin D.

A fourth staphylococcal enterotoxin was identified serologically with antiserum to the very crude enterotoxic products of growth of a strain which also produces enterotoxin C, and then with antiserum to the considerably purified enterotoxic antigen of a strain which produces only the new enterotoxin. The identification of this antigen as enterotoxin D was based on the following observations. It was produced by strains which do not produce enterotoxins A, B, or C; it was absent in the growth products of nonenterotoxigenic strains; when appreciably purified, it was associated with emetic activity in the cat, and its biological activity was neutralized only by antisera containing its specific antibody and not by antibodies to enterotoxins A, B, and C. Staphylococcal strain 494 (ATCC 23235) was selected as the prototype strain. The production of this enterotoxin alone and together with enterotoxin A by strains of food-poisoning origin indicates that its role in food poisoning is second in frequency only to that of enterotoxin A. The incidence of production of enterotoxins A, B, C, and D, and of unidentified cat emetic substances by strains from several source categories, is presented.