Fig. 3. ThfT confers SXT resistance in the presence of exogenous THF.

a Dose-response curves for the impact of exogenous THF on SXT resistance of M6^JRS4, TB08 and TB08-2-14. MICs are expressed as a percentage the maximum resolution of the Etest assay (32 μg/ml). Data from three biological replicates on MHF-Bm agar are presented as mean values ± SD. EC₅₀ values were calculated using Graphpad Prism software. b Representative Etest assays on MHF-Bm agar for data presented in a. c Schematic showing predicted effect of increased ThfT expression in TB08-2-14 on competition with other ECF S components for ECF transport modules and the effect on SXT MICs. Under conditions of low ThfT expression and low exogenous THF, competition between THF-loaded ThfT and S components loaded with other compounds limits THF import, resulting in low SXT MICs (top left). This competition is overcome by increased ThfT expression (top right) or increased extracellular THF, which results in high SXT MICs. Source data for panel a is provided as a Source Data file.