Effects of quercetin, baicalein, azithromycin, and their combination on biofilm formation, virulence factors and gene expression associated with Pseudomonas aeruginosa quorum sensing

BACKGROUND: Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen commonly associated with acute and chronic hospital-acquired infections. Its ability to form biofilms, regulated in part by quorum sensing, contributes to its persistence and resistance. Classified as a critical priority pathogen by the World Health Organization, there is an urgent need for new therapeutic strategies. In this study, we evaluated the effects of quercetin, baicalein and azithromycin, alone and in combination, on biofilm formation, virulence factor production, and quorum sensing gene expression in P. aeruginosa PAO1. METHODS AND RESULTS: The minimum inhibitory concentration of each compound was measured. The effect of each compound and their combinations on biofilm formation, elastases, pyocyanin and rhamnolipids were evaluated by spectrophotometric assays, and on lasR and mvfR gene expression by RT-qPCR. The minimum inhibitory concentrations of quercetin, baicalein and azithromycin were > 250, 62, and 16 µg/mL, respectively. The individual compound with the lowest percentage of biofilm formation was quercetin, followed by azithromycin and baicalein with 33%, 48%, and 51%, and the best combination was azithromycin-baicalein with 35%. Azithromycin and the mentioned combination showed the lowest production of elastases, pyocyanin and rhamnolipids (39% and 34%; 8% and 13%; 19% and 16%, respectively) and resulted in lasR and mvfR gene expression levels of 32% and 34%. CONCLUSIONS: The combination of azithromycin-baicalein showed inhibitory effects on biofilm formation, virulence factors and gene expression of lasR and mvfR. These findings highlight the potential of combining natural products with antibiotics as a promising strategy to attenuate virulence and disrupt quorum sensing-regulated behaviors in P. aeruginosa.