Fig. 4.

A metabolic feedback loop amplifies SMX-TMP activity. a, b SMX-TMP synergy was assessed by growth kinetics in the presence of a sub-inhibitory concentration of each drug and in combination. The results represent the mean and SD of three biological replicates. a Wild type (E. coli BW25113 strain) was grown in the presence of SMX (0.06 µg ml⁻¹), TMP (0.125 µg ml⁻¹), or a combination of SMX (0.06 µg ml⁻¹) and TMP (0.125 µg ml⁻¹). b ΔnudB (E. coli BW25113 ΔnudB) was grown in the presence of SMX (0.003 µg ml⁻¹), TMP (0.0125 µg ml⁻¹), or a combination of SMX (0.003 µg ml⁻¹) and TMP (0.0125 µg ml⁻¹). c SMX-TMP synergy against ΔnudB (E. coli BW25113 ΔnudB) was assessed by FICI. FICI_m, minimum value of FICI for the tested combinations is shown. Representative data from at least three independent experiments are shown. d Relative metabolite abundance and metabolic flux are shown. No drug treatment (i), sub-inhibitory concentrations of each drug (ii), and combination of sub-inhibitory concentrations of each drug (iii). SMX treatment inhibits the accumulation of DHF by TMP that results in potentiation of TMP activity, and TMP treatment decreases DHPPP that potentiates SMX activity. Cyclic mutual potentiation results in amplified depletion of the essential cofactor THF