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Int J Tryptophan Res
2019 Feb 27;12:1178646919831677. doi: 10.1177/1178646919831677.
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Tryptophan Silver Nanoparticles Synthesized by Photoreduction Method: Characterization and Determination of Bactericidal and Anti-Biofilm Activities on Resistant and Susceptible Bacteria.
Abstract
The high rates of antibiotics use in hospitals have resulted in a condition where multidrug-resistant pathogens have become a severe threat to the human health worldwide. Therefore, there is an increasing necessity to identify new antimicrobial agents that can inhibit the multidrug-resistant bacteria and biofilm formation. In this study, antibacterial and anti-biofilm activities of tryptophan silver nanoparticles (TrpAgNP) were investigated. The TrpAgNPs were synthesized by photoreduction method, and the influence of irradiation time and concentration of reagents were analyzed. The nanoparticles were characterized by transmission electron microscopy, Zeta Potential and (UV)-absorption spectra. The antibacterial activity of TrpAgNPs was tested for antibiotic-resistant and susceptible pathogens, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Citrobacter freundii, Klebsiella pneumoniae, Salmonella typhimurium, and Pseudomonas aeruginosa, evaluating the influence of photoreduction parameters in bactericidal effect. The results have shown that TrpAgNPs solutions with lower tryptophan/silver nitrate (AgNO3) ratio and higher AgNO3 concentration have higher bactericidal action against bacteria with inhibition of ~100% in almost all studied bacterial strains. The antimicrobial activity of TrpAgNPs within biofilms generated under static conditions of antibiotic-resistant and susceptible strains of S. aureus, S. epidermidis, E. coli, K. pneumoniae, C. freundii, and P. aeruginosa was also investigated. The results showed that TrpAgNPs have an inhibitory effect against biofilm formation, exceeding 50% in the case of Gram-negative bacteria (E. coli, K. pneumoniae, C. freundii, and P. aeruginosa-54.8% to 98.8%). For Gram-positive species, an inhibition of biofilm formation of 68.7% to 72.2 % was observed for S. aureus and 20.0% to 40.2% for S. epidermidis.
Figure 1. UV-Vis spectra of TrpAgNPs before and after different exposure times of the Xenon lamp (5, 10 and 15 minutes) for samples (A) TrpAg1, (B) TrpAg 2, (C) TrpAg 3, and (D) TrpAg 4.Inset figure shows multi-peaks fit for SPR band and electron microscopy image for TrpAg4 irradiated by 15 minutes.
Figure 2. Transmission electron microscopy image of (A) TrpAg1, (B) TrpAg2, (C) TrpAg3 and (D) TrpAg4 (Xe 10 minutes).
Figure 3. Size distribution histogram obtained for the sample TrpAg2 illuminated with Xenon lamp by 10 minutes.
Figure 4. Antimicrobial activity of TrpAgNPs against Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis, Escherichia coli ATCC 25922, E. coli O44:H18 042 (EAEC), Citrobacter freundii, Klebsiella pneumoniae, Salmonella Typhimurium ATCC 14028, and Pseudomonas aeruginosa ATCC 27853 after 24 hours of incubation with different concentrations and irradiation times of TrpAgNPs indicated in the Table 1. The error bar denotes the standard error.
Figure 5. Average percentage inhibition of biofilm formation. Semi-quantitative biofilm inhibition assay was performed using TrpAgNPs against Escherichia coli ATCC25922, Klebsiella pneumoniae, Pseudomonas aeruginosa ATCC 27853, Citrobacter freundii, Escherichia coli O44:H18 042 (EAEC), Staphylococcus aureus ATCC 25923 and S. epidermidis. after 24 hours of incubation. The error bar denotes the standard error.
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