Browsing by Author "Fernando, S. S. N."

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Bacterial enzyme-mediated synthesis of silver nanoparticles and antimicrobial activity
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Peiris, M. M. K.; Gunasekara, T. D. C. P.; Jayaweera, P. M.; Fernando, S. S. N.
Extracellular synthesis of silver nanoparticles (AgNPs) using bacteria has been explored for their unique physicochemical properties. Studies have shown that nitrate reductase enzyme catalyzes the bioreduction of Ag+ to Ag0 and formation of AgNPs. The objective of this study was to detect the presence/absence of nitrate reductase enzyme in selected bacteria and to study the formation of AgNPs. The antimicrobial activity of the biosynthesized AgNPs was also examined. Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, Acinetobacter baumannii (confirmed clinical strain) and Staphylococcus aureus ATCC 25923 were cultured in Nutrient broth. After 72 h of incubation, AgNO3 was added into the culture supernatant. AgNP formation was confirmed by Energy Dispersive X-ray analysis (EDX) and Transmission Electron Microscopy (TEM). For the nitrate reductase assay, heavy inocula of the above selected bacteria were inoculated in Nitrate broth and incubated at 37°C for 24 h. One dropper full of sulfanilic acid and α-naphthylamine were added to each tube and the colour change was observed. If no color change was observed a small amount of zinc (Zn) powder was added and the color change was observed. Well-diffusion method was performed to study the antimicrobial activity of the synthesized AgNPs against E. coli ATCC 25922, S. aureus ATCC 25923, P. aeruginosa ATCC 27853, Candida albicans ATCC 10231 and selected clinical isolates of P. aeruginosa, S. aureus and C. albicans. Positive controls were 0.5% AgNO3 and chemically synthesized AgNPs (0.436 mg/ml). All biosynthesized AgNPs were spherical in shape. The average sizes of the NPs were 11.14 ± 6.59 nm (S. aureus-NPs 0.435 mg/ml), 11.71 ± 2.73 nm (P. aeruginosa-NPs 0.45 mg/ml), 12.87 ± 2.95 nm (E. coli-NPs 0.99 mg/ml) and 12.22 ± 2.45 nm (A. baumannii-NPs 0.665 mg/ml). In general, zones of inhibition (ZOIs) given for chemically synthesized AgNPs, were higher than biosynthesized NPs. According to the well diffusion results, AgNPs produced by S. aureus resulted in the largest ZOI against the selected pathogens. Biosynthesized AgNPs were highly effective against Gram negative bacteria compared to Gram positive bacterial and fungal species, as well as Candida albicans, which were opportunistic pathogens. A. baumannii, E. coli and S.aureus, except P. aeruginosa, gave red colour after adding the two reagents and when Zn dust was added to P. aeruginosa, no colour change was observed. AgNP synthesis with a narrow size distribution was observed for all tested bacterial strains. AgNPs of S. aureus gave highest ZOI. Nitrate reduction was observed with all organisms. Further characterization of NPs is required to study the physical properties of silver NPs
TiO2 nanoparticles from bakers’ yeast: a potent antimicrobial
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Peiris, M. M. K.; Gunasekara, T. D. C. P.; Jayaweera, P. M.; Fernando, S. S. N.
Titanium dioxide (TiO2) is commonly applied in food industry, cosmetics and pharmaceuticals due to its photocatalytic activity, stability, optical and electronic properties and biocidal activity. TiO2 nanoparticles (NPs) can be synthesized by conventional chemical, physical and biological methods. In this study, TiO2 NPs were biosynthesized using Baker’s yeast (Y-TiO2) and characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray analysis (EDX). Antimicrobial activity was studied using plate coating method with and without sunlight exposure. XRD pattern confirmed the formation of pure anatase TiO2 nanoparticles. The porous surface of yeast cells act as the site for Ti3+ nucleation. According to EDX data, Ti (Atomic percentage of 20.89%), O (70.95%), P (5.78%) and N (2.38%) were the key elements in the sample. TEM imaging revealed that the nanoparticles were spherical with an average size of 6.7 ± 2.2 nm. The photocatalytic activity of TiO2 NPs was studied by monitoring the degradation of Methylene blue dye. Fifty percent of dye degradation was observed within 15 min of UV exposure. This study is the first report on antimicrobial study of yeastmediated TiO2 NPs synthesized using TiCl3. Antimicrobial activity of TiO2 nanoparticles was high against selected Gram positive bacteria and Candida albicans compared to Gram negative bacteria in the presence or absence of exposure to sunlight. The percentage reduction of colony forming units (CFU/mL) after exposure to Y-TiO2 NPs following 30 min of sunlight exposure significantly reduced S . aureus ATCC 25923 (77%), MRSA clinical isolate (97%) and C . albicans ATCC 10231 (95%) compared to the control due to the photocatalytic activity. The percentage reduction of CFU/mL for gram negative bacteria P . aeruginosa ATCC 27853, E . coli ATCC 25922 and A . baumannii clinical isolate were 58%, 46% and 50% respectively after exposure to sunlight. Y-TiO2 NPs showed antimicrobial activity in the absence of exposure to sunlight under room conditions. After 30 min of contact with Y-TiO2 NPs, percentage inhibition of S . aureus (20%), MRSA (25%), C . albicans (74%), P . aeruginosa (30%), E . coli (26 %) and A . baumannii (23%) were lower compared to sunlight exposure. Sunlight exposure has enhanced antimicrobial activity of TiO2 NPs. The outcomes indicate the significant physical properties and the impact of yeast-mediated TiO2 nanoparticles as a novel antimicrobial.