The current spreading of nanomaterial applications supports the search for further possible functions of theses diminutive particles. The antibacterial potentiality of zinc oxide (ZnO) nanoparticles (NPs), compared with conventional ZnO powder, against nine bacterial strains, mostly foodborne including pathogens, was evaluated using qualitative and quantitative assays. ZnO NP was more efficient as antibacterial agent than powder. Gram‐positive bacteria were generally more sensitive to ZnO than Gram negatives. The exposure of Salmonella typhimurium and Staphylococcus aureus to their relevant minimal inhibitory concentrations from ZnO NP reduced the cell number to zero within 8 and 4 h, respectively. Scanning electron micrographs of the treated bacteria with NPs exhibited that the disruptive effect of ZnO on S. aureus was vigorous as all treated cells were completely exploded or lysed after only 4 h from exposure. Promising results of ZnO NP antibacterial activity suggest its usage in food systems as preservative agent after further required investigations and risk assessments.
PRACTICAL APPLICATIONS
Foodborne pathogen invasion is still a recurrent serious problem facing researchers and food industry overseers. The introduction of novel powerful antimicrobial agents is of great importance for the control of pathogenic bacteria, especially antibiotic‐resistant strains. Zinc oxide (ZnO) nanoparticle (NP) could be one of these potential alternatives. This study focused on ZnO NP because of its increasing presence in many marketable products and that supports its application in food industries as a reasonably safe agent. The demonstrated antibacterial activity of ZnO NP recommends its possible application in the food preservation field; otherwise it can be applied as a potent sanitizing agent for disinfecting and sterilizing food industry equipment and containers against the attack and contamination with foodborne pathogenic bacteria.
Cadmium-tolerant (6 mM) Aspergillus niger (RCMB 002002) biomass was challenged with aqueous cadmium chloride (1 mM) followed by sodium sulfide (9 mM) at 37°C for 96 h under shaking conditions (200 rpm), resulting in the formation of highly stable polydispersed cadmium sulfide nanoparticles (CdSNPs). Scanning electron microscopy revealed the presence of spherical particles measuring approximately 5 nm. A light scattering detector (LSD) showed that 100% of the CSNPs measure from 2.7 to 7.5 nm. Structural analyses by both powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the presence of cubic CdS nanoparticles (CdSNPs) capped with fungal proteins. These CdSNPs showed emission spectra with a broad fluorescence peak at 420 nm and UV absorption onset at 430 nm that shifted to 445 nm after three months of incubation. The CdSNPs showed antimicrobial activity against E. coli, Pseudomonas vulgaris, Staphylococcus aureus, and Bacillus subtilis, and no antimicrobial activity was detected against Candida albicans. The biosynthesized CdSNPs have cytotoxic activity, with 50% inhibitory concentrations (IC50) of 190 μg mL-1 against MCF7, 246 μg mL-1 against PC3, and 149 μg mL-1 against A549 cell lines.
An eco-friendly process for the silver nanoparticles (Ag-NPs) biosynthesis was investigated using the fungus Monascus purpureus as a safe and commercially used microorganism. M. purpureus growth filtrate was used for the reduction of the aqueous silver nitrate into Ag-NPs with almost 100% size range of 1-7 nm, which was considered as one of the smallest microbial biosynthesized Ag-NPs. The biosynthesized Ag-NPs were structurally characterized using UV, FTIR, DLS, TEM, and XRD. The biosynthesized Ag-NPs were stable after 3 months with no alteration in shape or size. M. purpureus showed no nitrate reductase activity, whereas its pigments reducing power was decreased after nanoparticles formation indicating its role in the Ag-NPs biosynthesis. The synthesized Ag-NPs exhibited strong antimicrobial activity against different bacteria and yeasts species. The anti-Candida activity of M. purpureus culture filtrate was enhanced in the presence of Ag-NPs; the maximum increase in microbial inhibition was observed against Candida albicans with 1.73 increased folds of inhibition zones, followed by their activity against C. tropicalis and C. glabrata with 0.919- and 0.694-folds of increase, respectively. The obtained results suggest that the biosynthesized Ag-NPs offers a promising cost-effective, eco-friendly, and an alternative way to the conventional method of synthesis that could have wide applications in medicine.
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