Investigation on enhanced antimicrobial activity and bactericidal mechanism of photoactivated luteolin against Listeria monocytogenes

This study investigated the antimicrobial mechanism of the natural flavonoid luteolin (LUT) as a novel photosensitizer in photodynamic inactivation (PDI) against Listeria monocytogenes (LM). Following 8-h UV-A activation, luteolin (LUT-UV, 0.8 mg/mL) exhibited markedly improved antimicrobial activity, resulting in 99.93 ± 0.03 % bacterial inactivation after 4-h co-incubation with LM suspension (1 × 10 8  CFU/mL), significantly higher the 87.77 % ± 0.89 % inactivation rate observed with LUT treatment alone. LUT-UV significantly increased reactive oxygen species (ROS) generation, enhanced bacterial membrane permeability, and aggravated intracellular content leakage. Scanning electron microscopy (SEM) observations confirmed that LUT-UV treatment caused significant damage to LM cells, including membrane shrinkage and rupture. Furthermore, RT-qPCR analysis revealed that LUT-UV significantly downregulated genes associated with hemolytic toxicity and biofilm formation in LM. The pepper contamination model experiment demonstrated that LUT-UV could effectively eliminate LM contamination. This study confirmed that LUT functions as both a photosensitizer and photoreceptor in PDI, demonstrated its potential applications in cold chain systems, and provided theoretical foundations for developing efficient and safe natural compound-based sanitizers.