Antibacterial activity and mechanism of action of ε-poly-l-lysine

•Antibacterial activity and mechanism of ε-PL against E. coli O157:H7 was investigated.•Critical inhibitory factors toward the growth of E. coli O157:H7 by ε-PL was analyzed.•Cell membrane integrity and cell morphology of E. coli O157:H7 was affected by ε-PL.•A positive correlation between reactive oxygen species levels and ε-PL concentration in E. coli O157:H7 cells.•ε-PL induced the expression of different genes related to oxidative/redox stress, SOS response, virulence. ε-Poly-l-lysine (ε-PL)2ε-Poly-l-lysine (ε-PL).2 is widely used as an antibacterial agent because of its broad antimicrobial spectrum. However, the mechanism of ε-PL against pathogens at the molecular level has not been elucidated. This study investigated the antibacterial activity and mechanism of ε-PL against Escherichia coli O157:H7 CMCC44828. Propidium monoazide-PCR test results indicated that the threshold condition of ε-PL for complete membrane lysis of E. coli O157:H7 was 10μg/mL (90% mortality for 5μg/mL). Further verification of the destructive effect of ε-PL on cell structure was performed by atomic force microscopy and transmission electron microscopy. Results showed a positive correlation between reactive oxygen species (ROS)3Reactive oxygen species (ROS).3 levels and ε-PL concentration in E. coli O157:H7 cells. Moreover, the mortality of E. coli O157:H7 was reduced when antioxidant N-acetylcysteine was added. Results from real-time quantitative PCR (RT-qPCR)4Real-time quantitative PCR (RT-qPCR).4 indicated that the expression levels of oxidative stress genes sodA and oxyR were up-regulated 4- and 16-fold, respectively, whereas virulence genes eaeA and espA were down-regulated after ε-PL treatment. Expression of DNA damage response (SOS response)5DNA damage response (SOS response).5 regulon genes recA and lexA were also affected by ε-PL. In conclusion, the antibacterial mechanism of ε-PL against E. coli O157:H7 may be attributed to disturbance on membrane integrity, oxidative stress by ROS, and effects on various gene expressions, such as regulation of oxidative stress, SOS response, and changes in virulence.