Naringin generates three types of reactive oxygen species contributing differently to apoptosis-like death in Escherichia coli

Aims: Naringin is a flavonoid with a polyphenolic structure which induces formation of reactive oxygen species (ROS). Although the antibacterial effect of naringin has been demonstrated, the mechanism underlying this effect has not yet been elucidated. We focused on investigating the antibacterial mode of action of naringin in Escherichia coli following ROS generation. The contributions of ROS, hydroxy radicals (OH-), super oxide (O-2(-)), and hydrogen peroxide (H2O2) were investigated. Main methods: ROS accumulation was detected using fluorescence dyes, and all experiments were conducted using the scavenger including tiron, sodium pyruvate, and thiourea to assess the contribution of each ROS. Western blotting assays were used to observe the activation of the SOS response for DNA repair. DNA frag-mentation, membrane depolarization, and phosphatidylserine exposure were estimated using TUNEL, DiBAC4(3), and Annexin V/PI. Key findings: Accumulation of ROS was observed in Escherichia coli after treatment with naringin. Oxidative stress induced cellular dysfunction including DNA damage, which results in SOS response activation. Eventually, apoptosis-like death occurred in cells treated with naringin. The cells had different contributions of each ROS and accompanying apoptotic factors. The ROS most destructive to E. coli was OH-, followed by H2O2 and O-2- . Significance: Due to its efficacy, naringin is a useful antimicrobial agent. An initial investigation into the anti-bacterial mode of action of naringin is presented in this paper. The contribution of each ROS to apoptosis-like cell death (ALD) was investigated, and the results enhanced our understanding of the correlation between the SOS response and oxidative stress in bacteria.