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 ۵۰ strains of S.typhi. Five Submic showed that sensitivity was higher among Submic ۱, ۲, and ۳ than those in Submic ۴ and ۵ that show higher resistance (۹۶%, ۹۴%, and ۸۶% vs. ۴%), respectively. By Microtiter plate when we used three diluted concentrations of silver nanoparticles of Submic ۱, ۲, and ۳, significant were found that after ۲۴ hours was significantly higher than that after ۴۸ hours, as Submic ۱ (۰.۱۹۸۷۴ ± ۰.۰۳۴۱۵۶ vs. ۰.۱۴۸۶۴ ±۰.۰۲۵۹۰۸), respectively with mean differences of ۰.۰۵۰۱۰۰ (t= ۹.۷۹۴, df: ۴۹, P=۰.۰۰۰) and the means of Submic ۲ and ۳ was (۰.۲۰۷۷۶ ± ۰.۰۳۱۱۹۷ vs. ۰.۱۵۷۳۰ ± ۰.۰۲۷۰۶۰) (t=۱۰.۴۰۱, df: ۴۹, P= ۰.۰۰۰) and (۰.۲۱۴۶۴ ± ۰.۰۳۰۷۹۳ vs. ۰.۱۶۸۰۲ ± ۰.۰۲۶۱۱۱) with mean differences of ۰.۰۵۰۴۶۰ and ۰.۰۴۶۶۲۰, respectively and (t= ۹.۰۳۱, df: ۴۹, P= ۰.۰۰۰, 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.

Keywords:

S.typhi , Silver nanoparticles , Synthesis , Mode of action