Figure 6.

Adrenaline modulates the ability of Salmonella to resist antimicrobial peptides. We tested the effect of pre-exposure to adrenaline on the ability of Salmonella to resist the antimicrobial peptide polymyxin B. Addition of adrenaline (50 μM) significantly reduced Salmonella survival during exposure to polymyxin B (0.15 μg ml^-1). This was fully reversed by the β-adrenergic blocker propranolol (500 μM). Sensitivity levels of the basS mutant (SL1344basS) to polymyxin B were very similar to those of the adrenaline-treated SL1344. Reversal of polymyxin B sensitivity by propranolol is dependent on the presence of basS. Experiments were repeated at least three times. Asterisk indicates significant difference by the student t-test. Standard error bars are shown. Water, H₂O; Adrenaline, ADR; Polymyxin B, PB; Propranolol, PO.