Effect of Internalin InlJ on Phage-Mediated Suppression of Intracellular Listeria monocytogenes Infection

This study aimed to elucidate the functional characteristics of internalin InlJ from Listeria monocytogenes (Lm) in adhesion, invasion, intracellular proliferation, and mitochondrial damage and to clarify its regulatory mechanism in phage-mediated control of intracellular Lm infection. The results indicated that the ability of an inlJ deletion strain of Lm NJ05, NJ05-ΔinlJ, to adhere to and invade Caco-2 cells decreased by 56.37% and 17.74%, respectively, and the intracellular proliferation capacity also significantly decreased compared with the parental strain. The absence of InlJ resulted in decreased accumulation of mitochondrial reactive oxygen species (ROS) without affecting the membrane potential, thereby reducing the cytotoxicity of Lm. However, the NJ05-ΔinlJ strain displayed heightened sensitivity to phage vB-LmoM-SH3-3, with its efficiency of plating (EOP) 1.37 times that of the wild-type strain, and showed substantially enhanced lytic activity in vitro. Pre-treatment of Caco-2 cells with the phage led to a significant reduction in their adhesion to and invasion by Lm and its intracellular proliferation, and effectively alleviated mitochondrial damage caused by Lm. Thus, InlJ, a newly identified member of the internalin family, acts as an important factor influencing mitochondrial damage and regulates the interaction between Lm and phages, laying the foundation for the application of phages in combating intracellular bacterial infections.