الفهرس 
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Abstract
The threat of antimicrobial resistance to human health is real. Morbidity and death are caused by pathogens such as multidrug-resistant bacteria and Candida. Furthermore, scientists have a significant difficulty in developing a new antimicrobial treatment to solve the problem of multidrug resistance.
Nanoparticles might be a promising solution since they can both destroy multidrug resistant microorganisms and function as transporters for medicines and natural antibacterial agents.
The purpose of this study was to control multi drug resistant microorganisms by zinc oxide nanoparticles synthesized using three aqueous plant extracts, rosemary leaves, lemon peels and pomegranate peels.
The obtained results can be summarized in the following points:
1. Thirteen of multi-drug resistant bacteria were isolated from different clinical samples ( urine, sputum, wound and blood samples) that were collected from Medical Microbiology and Parasitology laboratory in Nile Health Insurance Hospital, Cairo, Egypt. Eight of them were Gram negative bacilli and identified as K. pneumoniae (3 strains), E.coli (3 strains), P. aeruginosa (2 strains) and five were identified as Gram positive cocci Staphylococcus aureus. based on their morphological, cultural, biochemical and molecular characteristics.
2. Four clinical identified Candida strains including two Candida albicans, one Candida glabrata and one Candida krusei were also included in this study.
3. The three plant extracts, rosemary leaves, lemon and pomegranate peels were prepared and used separately for synthesis of zinc oxide nanoparticles from zinc acetate dehydrate.
4. Zinc oxide nanoparticles were characterized by using different techniques, UV-Vis Spectrophotometry, Transmission Electron Microscopy , Dynamic Light Scattering (DLS) and Fourier Transform Infrared Spectrum (FTIR) .
5. Antibacterial and antifungal activity of the three synthesized ZnONPs were evaluated by well diffusion method. Zinc oxide nanoparticles synthesized using rosemary leaves’ , lemon peels’ and pomegranate peels’ extracts have broad spectrum antimicrobial activities compared with anibiotics and antifungal agents, the ZnONPs synthesized using rosemary leaves’ extract showed the most significant activity against the tested bacterial strains with a maximum diameter of inhibition zone as follow: E. coli (21.33 mm) > K. pneumonia (19.43 mm)> P. aeruginosa (19.25 mm) > S. aureus (16.86 mm), ZnONPs synthesized using lemon peels’ extract showing a maximum activity against E. coli (19.33 mm) > K. pneumonia (19.22 mm) > P. aeruginosa (18 mm) > S. aureus (14 mm). ZnONPs synthesized using Pomegranate peels’ extract showed a maximum activity against K. pneumonia (20 mm) > E. coli (18 mm) > S. aureus (13.8 mm) >P. aeruginosa (13.5 mm). The results demonstrated that ZnONPs synthesized using lemon peels’ extract showed the maximum anticandidal activity against both C. glabrata (24.5 ± 0.5 mm) and C. albicans (19.5 ± 1.5mm), while rosemary leaves mediated synthesized ZnONPs showed maximum anticandidal activity against C.krusei (23.3 ± 0.6 mm). The antifungal activity of the three synthesized ZnONPs against C.albicans was as follow : ZnONPs synthesized using lemon peels’ extract < ZnONPs synthesized using pomegranate peels’ extract < ZnONPs synthesized using rosemary leaves’ extract, while with C.glabrata it was as follow: ZnONPs synthesized using lemon peels’ extract < ZnONPs synthesized using rosemary leaves’ extract < ZnONPs synthesized using pomegranate peels’ extract.
6. MIC, MBC and MFC assay of the three biosynthesized nanoparticles were evaluated in range values of 0.125-0.5 mg/ml for the tested microorganisms and also the ratio of MBC/MIC and MFC/MIC ranged 1 to 2 meaning that the effect of the three synthesized ZnONPs were considered as bactericidal and fungicidal.
7. Significant synergistic effect was detected in combining five antibiotics (Amikacin, Ampicillin / sulbctam, Cefotaxime, Norfloxacin and Ciprofloxacin) and antifungal agent (Itraconazole) with the biosynthesized ZnONPs against the tested multi drug resistant microorganisms, combining the biosynthesized ZnONPs with Amikacin and Ciprofloxacin not only showed significant synergistic effect against multi drug resistant microorganisms but also showed no antagonistic activity. More synergistic effect was detected when ZnONPs synthesized using lemon peels’ extract was combined with the tested antimicrobial agents.
8. Evaluation of antioxidant activity of the biosynthesized ZnONPs using rosemary leaves’ and pomegranate peels’ extracts showed (IC50) value of 60.9 ±0.0 and 713.71 ±34.73 µg/ml. Moreover ZnO NPs synthesized using lemon peel extract showed weak antioxidant action, in comparison with ascorbic acid (IC50 = 12 µg/ml) revealing the significant antioxidant activity of ZnONPs synthesized using rosemary leaves’ extract.
9. Cytotoxicity of the three synthesized ZnONPs using rosemary leaves’, lemon and pomegranate peels’ extracts against normal human lung fibroblast (CC50) values of 497 ±7.8, 230.12 ± 9.34 and 85.69 ± 4.13 µg/ml respectively , while their cytotoxicity against Hepatocellular carcinoma cells have half maximal inhibitory concentration (IC50) value of 212 ± 4.8, 106.24 ± 4.88 and 27.93 ± 1.65 µg/ml respectively indicating low anticancer activity of ZnONPs synthesized using rosemary leaves’, lemon peels’ and pomegranate peels’ extracts against cancer cells with significant low toxic effect against normal cell.