Quorum Sensing Inhibition and Virulence Factor Attenuation in Pseudomonas aeruginosa by Camphor

Abstract

Objectives: This study aimed to assess the inhibitory effects of camphor on quorum sensing (QS), virulence factors, and biofilm formation in Pseudomonas aeruginosa, a multidrug-resistant pathogen. Methods: P. aeruginosa was treated with sub-inhibitory concentrations of camphor (500, 250, and 125 µg/mL). Assays evaluated biofilm formation, surface hydrophobicity, swarming motility, cell aggregation, and exopolysaccharide (EPS) production. Inhibition of virulence factors—pyocyanin, rhamnolipid, protease, and chitinase—was also assessed. RT-PCR was used to quantify expression of QS-related genes (LasR, LasI, RhlR, and RhlI). Results: The minimum biofilm inhibitory concentration (MBIC50) ranged between 125 and 63 µg/mL. Camphor significantly reduced biofilm formation and virulence factor production at all tested concentrations. It also decreased EPS synthesis, swarming motility, hydrophobicity, and cell aggregation. Camphor suppressed acyl homoserine lactone (AHL) production and downregulated QS genes, reducing LasR and LasI expression by 5-fold and 4.6-fold, and RhlR and RhlI by 1.8-fold and 1.5-fold, respectively. Conclusion: Camphor demonstrates strong antibiofilm, antivirulence, and anti-QS activities against P. aeruginosa at concentrations as low as 125 µg/mL. These results suggest camphor is a promising candidate for alternative treatment strategies, warranting further investigation of its mechanisms and clinical safety.