الفهرس | Only 14 pages are availabe for public view |
Abstract In this study, eleven isolated lactic acid bacteria from food and Enterococcus hirae, Lactobacillus bulgaricus and Enterococcus faecium were used to biosynthesize titanium dioxide nanoparticles. E. hirae, L. bulgaricus and E. faecium with three bacterial isolates from molasses, fermenting olive brine and carrot had the ability to biosynthesize titanium dioxide nanoparticles. The three potent bacterial isolates were characterized morphologically, biochemically, genetically by 16S rRNA gene sequencing and identified as Enterococcus thailandicus, Enterococcus gilvus and Enterococcus durans. The biosynthesized TiO2 NPs were extracted and characterized by UV-Vis spectroscopy, Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis. UV- Vis spectrophotometer of biosynthesized TiO2 NPs showed single and strong absorption peak at 326 nm for E. hirae, 322 nm for L. bulgaricus, 324 nm for E. thailandicus, 323 nm for E. gilvus, 325 nm for E. durans and 328 nm for E. faecium. This band was called the surface Plasmon resonance (SPR) which demonstrated small and spherical nanoparticles. The mean particle size of the biosynthesized TiO2 NPs was estimated by TEM to be 24.9 nm for E.hirae, 16.3 nm for L. bulgaricus, 21.6 nm for E. thailandicus, 16.6 nm for E.gilvus, 24.36 nm for E.durans and 61.09 nm for E. faecium. FTIR spectrum was measured in a range of 500-4000 cm-1 to determine the chemical functional groups with specific peaks which were characteristic to TiO2 NPs. The XRD pattern proved that the biosynthesized nanoparticles were pure rutile TiO2 phase and the crystal structures (tetragonal structures) agree well with the corresponding reported ICDD data (International Centre for Diffraction Data) file no. 01-078-4185, 00-021-1276, 01-078-4188, 01-075-6234 and 01-076-0317. The peaks and their corresponding Bragg’s angles were regarded as an indicator of biologically synthesized TiO2 NPs crystallites. TiO2 NPs biosynthesized by E.hirae and L.bulgaricus were tested against various pathogenic micro-organisms causing food poisoning, Gram positive bacteria (Staphylococcus aureus and Bacillus cereus), Gram negative bacteria (Salmonella typhi and Escherichia coli) and pathogenic fungi (Penicillum spp, Aspergillus niger and Fusarium oxysporum) at concentrations (500 µg∕ml, 700 µg∕ml and 1 mg∕ml). It showed high antimicrobial activity against the tested microbes. The antimicrobial effect of TiO2 NPs on pathogenic micro-organisms was confirmed by Transmission Electron microscopy which used to investigate the mechanism part of action on bacterial and fungal cells. The cytotoxicity of Oral Epithelial cell (OEC) lines was studied using WST-1 assay for TiO2 NPs at various doses of concentrations 0.01 mg/ml, 0.1 mg/ml, 0.3 mg/ml, 1 mg/ml and 10 mg/ml. The cell viability of the oral epithelial cell lines decreased with increasing the concentration of TiO2 NPs (96.26 %, 83.16 %, 81.82 %, 76.94 % and 55.8 %) respectively. IC50 (the inhibition concentration at which half of the viable cells died) of the biosynthesized TiO2 NPs was greater than 10 mg/ml concentration. This indicated the non-toxic nature of the nanoparticles even at high concentration (10 mg/ml). So the green synthesized TiO2 NPs can be used as a potent antimicrobial agent to prevent food borne pathogens instead of chemical resistant antibiotics, and also can be involved in many applications. |