Antibacterial activity of l-EP against (A) E. coli CFT073 and (B) the fes mutant. Relative OD600 refers to the OD600 value of the treated sample divided by that of the untreated control; (mean ± standard deviation, n = 7 for CFT073, n = 8 for the fes mutant); statistical differences compared to untreated controls were calculated using two-tailed student t test assuming unequal variances; ****P < 0.0001, ***P < 0.001, **P < 0.01, *P < 0.05. All assays were performed in modified M9 medium at 30 °C for 11 h.