الفهرس 
Biological SynthesisOnly 14 pages are availabe for public view
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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.