Hesperetin is a naturally occurring flavonoid with reported antimicrobial activity, but its antibacterial modes of action remain poorly understood. In this study, the antibacterial effects of hesperetin in Escherichia coli were investigated. Hesperetin treatment increased intracellular reactive oxygen species (ROS) levels, and scavenger-based experiments supported the contribution to downstream effects. Elevated ROS was associated with membrane depolarization and oxidative membrane damage, including lipid peroxidation, as indicated by increased malondialdehyde levels. Hesperetin treatment also increased DNA damage, including chromatin condensation and DNA fragmentation. Because recA is a key regulator of the SOS DNA repair response, a recA-deficient strain was used to assess the role of SOS-associated repair signaling; DNA damage was significantly greater in the recA-deficient strain than in the wild-type strain. In addition, programmed cell death-like features, including phosphatidylserine externalization detected by Annexin V/PI staining, were observed. Collectively, these findings indicate that the antibacterial activity of hesperetin involves ROS-associated membrane injury, oxidative DNA damage, and recA-dependent SOS-associated responses, together with programmed cell death-like features in E. coli.
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