Photo-chemically activated silver nanoparticles (AgNPs): Analysis of antibacterial activity and possible mechanisms

Silver nanoparticles (AgNPs) are being investigated as promising antimicrobial agents. The purpose of this study was to investigate the antibacterial property of two novel, photo chemically synthesized silver nanoparticles, and to evaluate the potential antibacterial mechanisms involved. Using both optical density of liquid culture and colony counts we showed that photo-chemically synthesized, negatively charged (-) AgNPs made incorporating low molecular weight poly(acrylic acid) (PAA), were bactericidal. However, photo-chemically synthesized, positively charged (+) AgNPs made incorporating chitosan, had no evidence of any antibacterial activity beyond that of chitosan alone. The (-) AgNPs had antimicrobial activity against Gram-negative bacteria and Gram-positive bacteria. The antibacterial activity of (-) AgNPs was inversely correlated to NaCl and presence of added glucose. These (-) AgNPs showed cooperativity with kanamycin but not with ampicillin. Our findings support a model where multiple mechanisms of activity work in combination to control bacterial growth for these novel (-) AgNPs which could use against multiple drug resistant microorganisms.