lasR / rhlR Expression Linked to Quorum Sensing-Mediated Biofilm Formation in Pseudomonas aeruginosa Using Gold Nanoparticles Synthesized with Ethnobotanical Extracts

The rapid emergence of multidrug-resistant bacteria endangers the efficacy of antibiotics, which leads to the search for novel anti-infective measures that do not rely on antibiotics. Quorum sensing inhibition (QSI) presents potential in making straightforward approach in disrupting cell-to-cell communication in bacteria, thereby decreasing virulence factors such as biofilm formation. To assess QSI of gold nanoparticles conjugated with ethnobotanical extracts (AuNPs + CEs) against Pseudomonas aeruginosa, antibacterial activity was assessed as a preliminary test and AuNPs + CEs that exhibited antibacterial activity were not used in the biofilm formation assay to rule out antimicrobial decrease in biofilm formation. RNA of bacterial sample treated with AuNPs + CEs with biofilm formation inhibitory activity was subjected to gene expression analysis. The results revealed that all AuNPs + CEs used in the microtiter biofilm formation assay showed a significant decrease in biofilm formation in P. aeruginosa. Gene expression analysis of lasR and rhlR revealed that AuNPs + CEs that exhibited decrease in biofilm formation also have downregulated expression of lasR and rhlR, an indication of quorum sensing–mediated decrease in virulence. Furthermore, samples treated with AuNPs + CEs, showed lower expression of lasR compared to samples treated with only CEs. This result presents the role of gold nanoparticles in enhancing the delivery of bioactive compounds present in the ethnobotanicals, with QSI activity against P. aeruginosa. Hence, the result offers the potential of AuNPs + CEs in QSI of disease-causing human pathogens.