Determination of Antibacterial Activity of Silver Nanoparticles

The synthesized AgNPs were examined for antimicrobial activity by a standard agar diffusion method against different bacterial cultures, S. aureus, E. coli, and P. aeruginosa. An equal number of initial bacterial culture with 0.5 McFarland concentrations was sub-cultured on LB agar. An equal number of initial bacterial culture with 0.5 McFarland concentrations was sub-cultured on LB agar.

All three case study solutions including pure T. brevifolia extract, silver nitrate, and AgNP were diluted individually to obtain seven serial concentrations of titers as follows: (1/1): 50 mM, (1/2): 25 mM, (1/4): 12.5 mM, (1/8): 6.25 mM, (1/16): 3.1 mM, (1/32): 1.5 mM and (1/64): 0.75 mM. Several sets of three selected bacterial culture plates were provided. Equal volumes of 100 μL/well of each dilution were applied to a set of three selected bacterial cultures as described above. Same sets of three bacterial culture plates were considered without any additive material as well as with cephalexin standard antibiogram disks as negative and positive controls, respectively. All plates were evaluated after 24 hours incubation at 37°C. The inhibition zone of the bacteria was accurately measured by the caliper and the mean diameter of the bacterial inhibition zone. The comparison with positive and negative control was considered as an indicator of antibacterial activity evaluation.²⁵ Each assay was repeated three times as described previously.^26,27