Biogenic synthesis of Psidium guajava-mediated silver nanoparticles: A comprehensive antibiofilm and antivirulence study

In this study, at sub-MIC, the efficacy of green synthesized Psidium guajava-mediated silver nanoparticles (Pg@AgNPs) in inhibiting quorum sensing facilitated virulence factors and suppressing biofilm formation was evaluated against clinical multidrug resistant (MDR) isolates, specifically Chromobacterium violaceum MCC-2290 and Pseudomonas aeruginosa PAO1. The AgNPs were synthesized by adding the leaf extract to a solution of silver nitrate, and the reduction of Ag⁺ ions to Ag⁰ was confirmed by the appearance of brown color. The Pg@AgNPs were characterized using Fourier transform infrared (FTIR), UV/Vis spectroscopy, TEM, and XRD. The UV/Vis spectrum showed the characteristic absorption peak of Pg@AgNPs in the range of 350–480 nm. FTIR analysis substantiated the existence of functional groups implicated in the synthesis and stabilization of AgNPs. The XRD analysis elucidated the crystalline characteristics of the nanoparticles. The TEM images further confirmed the spherical shape and size of the nanoparticles, which ranged between 5 and 25 nm. The AgNPs demonstrated notable antibacterial efficacy against C. violaceum and P. aeruginosa. Moreover, the Pg@AgNPs effectively suppressed both biofilm formation and the production of quorum sensing-mediated virulence factors such as pyoverdin (77.2%), pyocyanin (78.12%), and violacein (83.4%). Additionally, the Pg@AgNPs demonstrated broad-spectrum activity against biofilm formation, showing the biofilm inhibition in C. violaceum and P. aeruginosa by 81.86% and 87.89%, respectively. Under light microscopy, it is also observed that Pg@AgNPs reduce the formation of biofilm in both tested bacteria. The present finding highlights the potential of green-synthesized AgNPs using P. guajava leaf extract as antimicrobial agents with potential applications in combating bacterial infections and biofilm-related diseases.