## 3 Results and Discussion
Meanwhile, in the presence of TiO\({}_{2}\) NPs, the activity was enhanced to 81.9% against _E. coli_ and 90.7% against _S. aureus_. Figure 8: Growth curves of tested bacteria in the presence TiO\({}_{2}\) NPs: (**a**) optical density, (**b**) cell viability. Figure 9: Growth of the tested bacteria in the presence of amoxicillin and TiO\({}_{2}\) NPs measured at 600 nm. The crystalline structure and the shape of TiO\({}_{2}\) NPs are both considered as the most important conditions that affect its physicochemical factors and therefore its antimicrobial activity [38]. The anatase crystalline structure of TiO\({}_{2}\) presents its highest photocatalytic and antimicrobial activities among other crystalline structures. The results showed that structure of anatase can produce OH' radicals in the photocatalytic reaction, which will help eliminate the bacteria walls [39]. The antibacterial activity of the TiO\({}_{2}\) NPs mixed with amoxicillin was tested against _E. coli_ and _S. aureus_ utilizing the agar well diffusion method. Figure 11 shows the inhibition zones against _E. coli_ and _S. aureus_. It was noticed that TiO\({}_{2}\) NPs improved the activity of amoxicillin, and a higher concentration of nanoparticles had the best eliminating effect along with amoxicillin. The synergetic impact of nanoparticles mixed with amoxicillin was observed via the increase in inhibition zones, as illustrated in Table 2. This is due to the reaction between antibiotics molecules and nanoparticles; these nanoparticles contain hydroxyl groups, which easily react with the antibiotic. Thus, nanoparticles work as an antibiotic carrier and their antibacterial effect can be used. These results correspond to those of [PERSON] et al., who reported that TiO\({}_{2}\) nanoparticles in combination with the antibiotic ceftazidine (CEZ) had an excellent synergistic impact against _Pseudomonas_ spp. [40]. Furthermore, TiO\({}_{2}\) and ZnO nanoparticles have shown to promote the antibacterial activity of 8 mm against bacteria (_S. aureus_--ATCC 25923) and (_E. coli_--ATCC 25922) [41]. Figure 11: The antibacterial activity of TiO\({}_{2}\) NPs with (**A**) amoxicillin against _E. coli_, and (**B**) _S. aureus_. A (yellow color): amoxicillin used as control, while 1,2, and 3 were 400, 600, and 1000 ug mL\({}^{-1}\), respectively. Figure 10: Inhibition rate (%) of the tested bacteria in the presence of TiO\({}_{2}\) NPs, amoxicillin alone and a combination of amoxicillin and TiO\({}_{2}\) NPs. Several studies suggested the possible mechanisms involving the interaction of nanomaterials with biological molecules. It is believed that microorganisms carry a negative charge while metal oxides carry a positive charge. This creates an \"electromagnetic\" attraction between the microbe and treated surface. Once the contact is made, the microbe is oxidized and dies instantly [42; 43]. This synergism may cause cell inactivation at the regulatory network and signaling levels, decrease the activity of the respiratory chain, and inhibit the ability to assimilate and transport iron and phosphorous. These processes with the extensive cell wall and membrane alterations were the main factors that explain the biocidal activity of TiO\({}_{2}\) NPs.