FIG 5.

Indole can directly reduce bacterial heat tolerance. (A) Precultures of WT and the ΔtnaA mutant were diluted in fresh TSB to obtain approximately 10⁸ CFU/ml and subjected to heat tolerance analysis (55°C, 5 min) with several final concentrations of indole (approximately 0 to 2.0 mM). (B) Isolated persister cells of WT and the ΔtnaA mutant were resuspended in fresh TSB with or without 2.0 mM indole to obtain approximately 10⁵ CFU/ml and subjected to heat tolerance assay (57°C, 5 min). (C) The preculture of S. Typhimurium was diluted in fresh TSB with or without 2.0 mM indole to obtain approximately 10⁸ CFU/ml and subjected to heat tolerance analysis (55°C, 5 min). Data points represent means of results from at least three independent experiments, and error bars indicate standard deviations. Significant differences between indole⁻ and indole⁺ data were analyzed by t test (*, P < 0.05).