Biosynthesized silver nanoparticles at subinhibitory concentrations as inhibitors of quorum sensing, pathogenicity, and biofilm formation in Pseudomonas aeruginosa PAO1

<i>Pseudomonas aeruginosa</i> infections associated with biofilm are a significant clinical challenge due to the limited efficacy of traditional antibiotics or combination therapies. Hence, exploring novel strategies and assessing different compounds for their anti-biofilm or anti-quorum sensing (QS) properties is imperative. One of the various applications of silver nanoparticles (AgNPs) is to use them as an antimicrobial agent to target bacteria resistant to common antibiotics. This study evaluates the anti-biofilm and anti-virulence effect of biosynthesized AgNPs against <i>P. aeruginosa</i> PAO1 at subinhibitory concentration levels. Minimum inhibitory concentrations (MICs) and biofilm formation capacity were evaluated by the microdilution method and crystal violet method, respectively. Motility assay and virulence factors were investigated in the presence of AgNPs. It was observed that green-synthesized AgNPs at sub-MIC (50 μg/mL) suppressed <i>P. aeruginosa</i> biofilm formation by 78 %. Increased dose-dependent inhibitory effects on virulence phenotypes (LasB elastase, LasA protease, pyocyanin, and motility) regulated by QS were observed. In addition, the relative expression levels of biofilm-related genes including <i>algC, pslA</i>, and <i>pelA</i> were analyzed using RT-qPCR. The expression level of QS-regulated biofilm genes after AgNPs treatment sub-MIC led to a decrease in the expression of <i>algC, pslA,</i> and <i>pelA</i> by 77 %, 83 %, and 68 %, respectively. The findings of this study demonstrated how green AgNPs can effectively inhibit QS at sub-MIC concentrations, indicating their potential as antivirulence agents to deal with challenges related to biofilm formation and antimicrobial resistance in <i>P. aeruginosa</i>. This presents a promising alternative to traditional antibiotics in antimicrobial therapy.