Biological Synthesis and Structural Characterization of Selenium Nanoparticles and Assessment of Their Antimicrobial Properties
Biological synthesis of selenium nanoparticles (SeNPs) using microorganisms has received profound interest because of their potential to synthesize nanoparticles of various size, shape and morphology. In the current study, 206 selenium resistant bacterial isolates were isolated from 18 samples from different environmental sources of Saudi Arabia. Among These isolates, bacterial strain BGRW was selected on the basis of its ability to produce stable extra/intracellular SeNPs. Molecular characterization of this isolate indicated that BGRW strain belongs to the Providencia vermicola. BGRW was found to be highly resistant to selenium dioxide up to 20 mM.The biosynthesis of SeNPs was monitored by UV–Visible spectrum that showed surface plasmon resonance (SPR) peak at 295 nm. Further characterization of synthesized SeNPs was carried out using the XRD, TEM and FTIR spectroscopy. TEM and XRD analysis revealed that the SeNPs synthesized by BGRW was hexagonal in shape with a size range of ∼3 to 50 nm with average 28nm. FTIR spectroscopy confirmed the presence of proteins as the stabilizing agent surrounding the nanoparticles. In the present study six antibiotics were investigated to explore their synergistic effect when combined with SeNPs against various pathogenic. All tested antibiotics showed synergistic inhibition against a growth of the pathogenic bacteria. The biocide actions of SeNPs on Gram-negative and Gram-positive pathogens were studied using SEM. The results showed damage, blebs, fusion, clumps and randomly distribution in the cell wall of the tested microbes resulting the death of cells.
The MIC 90 of SeNPs was 10μg/mL, 15μg/mL and 20μg/mL for Staphylococcus aureus, Bacillus cereus and Escherichia coli respectively. The effect of SeNPs on the prevention and removing of biofilm were also studied, the antibiofilm concentration of SeNPs was 12μg/mL against Salmonella enteritidis and B. cereus, 16μg/mL against S. aureus and E. coli while the antibiofilm concentration was 18μg/mL against Proteus sp. and Peudomonas aeruginosa. Although the biogenic SeNPs had antimicrobial and antibiofilm effects, they did not show significant ability to remove the established biofilm up to 32μg/mL. The concentration of 24μg/mL showed a slight effect on removing the established biofilm. The antibiofilm effect of the combination of SeNPs with amoxicillin was investigated against six bacterial biofilms and result show a synergistic effect at a lower than the antibiotic or SeNPs minimum antibiofilm concentrations.
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