Study of Antimicrobial Activity of Silver Nanoparticles Against Salmonella Typhi Infections in Vitro

The aim of this study is to investigate the antibacterial effect of silver nanoparticles (AgNPs) against multidrug-resistant Salmonella typhi recovered from blood, stool, and fluid specimens. In vitro the antimicrobial activity of silver nanoparticles against S.typhi isolates done by determination of silver nanoparticles activity by agar wells diffusion assay, MIC, sub MIC, and by Microtiter plate (Submic). By agar wells diffusion assay and MIC, the antimicrobial activity of silver nanoparticles showed an inhibition zone, among 50 strains of S.typhi. Five Submic showed that sensitivity was higher among Submic 1, 2, and 3 than those in Submic 4 and 5 that show higher resistance (96%, 94%, and 86% vs. 4%), respectively. By Microtiter plate when we used three diluted concentrations of silver nanoparticles of Submic 1, 2, and 3, significant were found that after 24 hours was significantly higher than that after 48 hours, as Submic 1 (0.19874 ± 0.034156 vs. 0.14864 ±0.025908), respectively with mean differences of 0.050100 (t= 9.794, df: 49, P=0.000) and the means of Submic 2 and 3 was (0.20776 ± 0.031197 vs. 0.15730 ± 0.027060) (t=10.401, df: 49, P= 0.000) and (0.21464 ± 0.030793 vs. 0.16802 ± 0.026111) with mean differences of 0.050460 and 0.046620, respectively and (t= 9.031, df: 49, P= 0.000, respectively. Antibacterial activity of silver nanoparticles has been demonstrated in several investigations, but the reported MIC values range through a wide extent of variation. In our study, silver nanoparticles showed a good antibacterial activity against all the tested pathogens. The results of MIC and Submic tests revealed a higher MIC value for S.typhi compared with the other tested pathogens. It is possible that AgNPs act similarly to the antimicrobial agents used for the treatment of MDR S.typhi infections, which show four different mechanisms of action including: interference with cell wall synthesis, inhibition of protein synthesis, interference with nucleic acid synthesis, and inhibition of the metabolic pathway.