Antimicrobial activity of silver NPs

The antimicrobial action was determined by agar well diffusion assay. Antibacterial action was tested for synthesized Ag NPs and cell free supernatant against opportunistic pathogens of Gram-positive bacteria (Staphylococcus aureus ATCC 25923, S. epidermidis ATCC 12228, Bacillus cereus ATCC 11778), Gram-negative bacteria (Pseudomonas aeruginosa ATCC 9027, Proteus vulgaris ATCC 6896, Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 10031, Salmonella enterica NCTC 6017, Shigella sonnei GICK 337, S. flexneri GICK 233169), and yeast (Candida albicans UCM Y-1918) on Mueller–Hinton (MH) agar plates. Agar wells of 6 mm diameter were prepared and loaded with 50 μL of Ag NPs solution and 50 μL of bacterial cell suspension without AgNO₃ as control. The plates were incubated at 37°C for 24 h and the diameter of zone of inhibition was measured as indicated by clear area devoid of growth of test-strains. Each experiment was done twice.