Chromosomal locus for staphylococcal enterotoxin B

Abstract

The genetic locus of staphylococcal enterotoxin B (SEB) was investigated in the Staphylococcus aureus food-poisoning isolates, strains S6 and 277. Direct neutral sucrose gradient centrifugation analysis of sodium dodecyl sulfate-sodium chloride-mediated cleared lysates demonstrated that strain S6 contained a single 37S plasmid. Transductional analysis revealed that the 37S plasmid in S6 encoded for cadmium resistance (Cad) but not SEB. Additionally, elimination of cadmium resistance in S6 provided a plasmid-negative derivative that produced SEB at the same level as the parent. Examination of strain 277 showed two plasmids, a 37S species encoding for penicillin resistance (Pen(r)) and a 21S species containing the gene(s) responsible for tetracycline resistance (Tet(r)). Elimination of the 37S, pen(r)-plasmid in 277 had no effect on SEB production, whereas introduction of the 21S tet(r)-plasmid via transformation into strain 8325 (SEB-) did not confer enterotoxigenesis upon the transformants. The data obtained in this investigation suggest that the SEB gene(s) in these food-poisoning isolates of S. aureus is chromosomal.