FIG 8.

In vitro intracellular tryptophan concentrations vary significantly for reference strain F/IC-Cal3 compared with clinical strains F I-IV. (A and B) Ct-infected HeLa cells were incubated with either tryptophan-free DMEM medium (−Trp) (A) or complete medium treated with IFN-γ (+IFN-γ) (B) (see Materials and Methods). The medium was supplemented with indole (−Trp +Indole or +IFN-γ +Indole) or tryptophan (−Trp +Trp or +IFN-γ +Trp) as indicated. Infected cells were harvested at 48 hpi, and intracellular tryptophan concentrations were measured using high-pressure liquid chromatography-linked tandem mass spectrometry (see Materials and Methods). Data are presented as the mean tryptophan concentration (in picomoles) normalized to Ct 16S rRNA plus SD based on two independent experiments. *, P < 0.05; **, P < 0.01; ****, P < 0.0001.