FIGURE 4.

The ability of AMPs to activate PhoP-PhoQ as determined by the reporter gene assay. S. typhimurium ATCC 14028 WT (black bars) and null mutant (gray bars) were grown in LB-containing peptide at 0.25-fold MIC of the tested strain. After 6 (A) and 20 h (B) of incubation at 37 °C, 20 μl were sampled from each well and assayed for β-galactosidase (β-gal) expression. The experiments were performed in quintuplet, and their mean values were calculated. The results are expressed as the fold inductions relative to the control value of normal culture in the absence of peptide. The noninducer gentamicin was used as a control antibiotic. The error bars represent the standard error.