Synthesis and Evaluation of Quorum Quenching activity of Ag, TiO2 and ZnO metal nanoparticles against wild type and mutant strains of Chromobacterium violaceum

Abstract

The conventional strategies to combat pathogenic microbes seem to be inefficient to curb the menace of pathogens. The bacterial biofilm is a product of the quorum sensing (QS) process mediated by acylhomoserine lactones (AHL) in many pathogens. The QS inhibitors or quorum quenching (QQ) molecules that disrupt bacterial communication offer an alternative promising strategy to lower antibiotic resistance in pathogens. The nanoparticles can exhibit QQ potential that interrupts cell-to-cell communication. In the present study, laboratory synthesized metal-based nanoparticles such as silver (Ag), titanium oxide(TiO2) and zinc oxide (ZnO) were characterized using powder X-Ray diffractometer, UV-Visible spectroscopy, EDS, Cyclic voltammetry and TEM imaging technique. Ag and TiO2 nanoparticles were synthesized by the green synthesis method in the form of quantum dots, which was evidenced from TEM images on a less than 7nm scale. Silver quantum dots with size variation from 2.4nm to 4.2nm and TiO2 with size ranging from 4.9nm to 8.5nm were detected. The synthesized nanoparticles were elucidated for their potential as QQ by employing both wild and mutant strains of Chromobacterium violaceum. Nanoparticles affected violacein pigment production in both the strains of C. violaceum. Lower concentrations of NPs did not show any considerable effect on the AHLdependent Quorum sensing system, however, at moderate to higher concentrations, metal NPs exhibit Quorum Q activity. Higher concentrations of AgNPs and ZnONPs (i.e. 250 ppm and above) show cell inhibitory activity. In the percent pigment(violacein) inhibition assay, maximum pigment inhibition was detected at a concentration range of 100-125ppm in both the strains of C. violaceum without inhibiting cell growth. In the case of TiO2NPs, maximum pigment inhibition was detected at 500ppm without affecting cell growth in both the strains of C. violaceum. The percent pigment inhibition observed in all nanoparticles was nearly similar in both strains of C. violaceum indicating that the mechanism of action of pigment inhibition is due to interference at the reception of the AHL signaling molecule.