Investigation the potential use of silver nanoparticles synthesized by propolis extract as N-acyl-homoserine lactone-mediated quorum sensing systems inhibitor

Background/aim: Quorum sensing (QS) is a chemical communication process that bacteria use to regulate virulence. Inhibition of QS (antiQS) overcomes the pathogenicity of bacteria. Silver nanoparticles (AgNPs) have been used as antimicrobials against pathogens, but have not been used against QS-mediated bacterial infection. Also, studies have been carried out on the inhibitory effects of propolis based structures on pathogen growth, but no studies have been found on their potential use as QS inhibitor. The present study aims to investigate the synthesis and characterization of silver nanoparticles (AgNPs) reduced with propolis extract (P-AgNPs) and evaluation of their antimicrobial and, for the first time, antiQS activity. Materials and methods: P-AgNPs were synthesized using with different volumes (1, 2.5 and 5 mL) of propolis extract (PE) by biological method via reduction of silver nitrate. Synthesized P-AgNPs were characterized in terms of hydrodynamic, chemical, morphological, physical, and antioxidant properties. Disc diffusion and flask incubation assays were used to evaluate the antimicrobial effect against Gram-negative bacteria (Escherichia coli, Proteus mirabilis, Proteus vulgaris, Salmonella typhimurium, Enterobacter aerogenes, Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus, Streptococcus mutans, Bacillus thuringiensis) and QS-regulated biofilm activity against biosensor strain Chromobacterium violaceum CV026. Results: AgNPs were successfully synthesized by biological method via PE. The violacein pigment production based on the QS system was greatly inhibited by the P-AgNPs (inhibition zones: 16.22-21.48 mm and violacein inhibition: 63.16 +/- 2.4-75.24 +/- 3.5 %) without interfering with the growth of bacteria, which is the first report on the antiQS effect of P-AgNPs. Conclusion: Our results suggest that P-AgNPs may be potentially used to inhibit bacterial physiological processes due to the signal molecules regulates important collective behavior of bacteria. The development of such nontoxic biomaterials may have great potential to evaluate for the new medicinal substance that inhibits the pathogenic biofilms.