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

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Abstract
More than 80 percent of TSST-l-positive strains of Staphylococcus aureus are tryptophan auxotrophs (Trp−). Chromosomal mapping has located the genetic determinant for TSST-l (tst) in the trp operon for strain S411 (Trp−) and near the tyrE site for strain FRIl169 (Trp+). Auxonographic screening on tryptophan-free medium of 28 strains of S. aureus (TSST-l-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-l production. Cocultivation of strain FRIll69 or S411 with E. coli strain 7877 showed that TSST-l production by FRI1169 was not enhanced. In contrast, TSST-l production by S411 was equal to that of S. aureus alone (12,000 ng/mL) if the input loglO cfu of S. aureus was of equal or greater ratio to input E. coli and if the recovered S. aureus was >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.

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