Growth of Toxic Shock Syndrome Toxin I-Producing, TryptophanRequiring Strains of Staphylococcus aureus Associated with the Presence of Escherichia coli

More than 80 percent of TSST-1-positive strains of Staphylococcus aureus are tryptophan auxotrophs (Trp-). Chromosomal mapping has located the genetic determinant for TSST-1 (tst) in the trp operon for strain S411 (Trp-) and near the tyrB site for strain FRI1169 (Trp*). Auxonographic screening on tryptophan-free medium of 28 strains of S. aureus (TSST-1-positive and -negative, Trp+ and Trp-) against Escherichia coli (strains 6094, 7603, and 7877) and other strains of Enterobacteriaceae showed that Trp- S. aureus strains responded only to E. coli and tryptophan. Neither E. coli nor tryptophan inhibited TSST-1 production. Cocultivation of strain FRI1169 or S411 with E. coli strain 7877 showed that TSST-1 production by FRI1169 was not enhanced. In contrast, TSST-1 production by S411 was equal to that of S. aureus alone (less than 640 ng/mL) or enhanced (greater than 12,000 ng/mL) if the input log10 cfu of S. aureus was of equal or greater ratio to input E. coli and if the recovered S. aureus was greater than log10 5 cfu. These results suggest that nutritionally deficient toxicogenic strains of S. aureus may overcome growth limitation by coexisting in dynamic balance with strains of E. coli.