Mutation of <i>Pseudomonas aeruginosa lasI/rhlI</i> diminishes its cytotoxicity, oxidative stress, inflammation, and apoptosis on THP-1 macrophages

The management of <i>Pseudomonas aeruginosa</i> (<i>P. aeruginosa</i>) infections presents a substantial challenge to clinics and public health, emphasizing the urgent need for innovative strategies to address this issue. Quorum sensing (QS) is an intercellular communication mechanism that coordinates bacterial activities involved in various virulence mechanisms, such as acquiring host nutrients, facilitating biofilm formation, enhancing motility, secreting virulence factors, and evading host immune responses, all of which play a crucial role in the colonization and infection of <i>P. aeruginosa</i>. The LasI/R and RhlI/R sub-systems dominate in the QS system of <i>P. aeruginosa</i>. Macrophages play a pivotal role in the host's innate immune response to <i>P. aeruginosa</i> invasion, particularly through phagocytosis as the initial host defense mechanism. This study investigated the effects of <i>P. aeruginosa</i>'s QS system on THP-1 macrophages. Mutants of PAO1 with <i>lasI/rhlI</i> deletion, as well as their corresponding complemented strains, were obtained, and significant downregulation of QS-related genes was observed in the mutants. Furthermore, the <i>ΔlasI</i> and <i>ΔlasIΔrhlI</i> mutants exhibited significantly attenuated virulence in terms of biofilm formation, extracellular polymeric substances synthesis, bacterial adhesion, motility, and virulence factors production. When infected with <i>ΔlasI</i> and <i>ΔlasIΔrhlI</i> mutants, THP-1 macrophages exhibited enhanced scavenging ability against the mutants and demonstrated resistance to cytotoxicity, oxidative stress, inflammatory response, and apoptosis induced by the culture supernatants of these mutant strains. These findings offer novel insights into the mechanisms underlying how the <i>lasI/rhlI</i> mutation attenuates cytotoxicity, oxidative stress, inflammation, and apoptosis in macrophages induced by <i>P. aeruginosa</i>.IMPORTANCE<i>P. aeruginosa</i> is classified as one of the ESKAPE pathogens and poses a global public health concern. The QS system of this versatile pathogen contributes to a broad spectrum of virulence, thereby constraining therapeutic options for serious infections. This study illustrated that the <i>lasI/rhlI</i> mutation of the QS system plays a prominent role in attenuating the virulence of <i>P. aeruginosa</i> by affecting bacterial adhesion, biofilm formation, extracellular polymeric substances synthesis, bacterial motility, and virulence factors' production. Notably, THP-1 macrophages infected with mutant strains exhibited increased phagocytic activity in eliminating intracellular bacteria and enhanced resistance to cytotoxicity, oxidative stress, inflammation, and apoptosis. These findings suggest that targeted intervention toward the QS system is anticipated to diminish the pathogenicity of <i>P. aeruginosa</i> to THP-1 macrophages.