3.2.2. Antibacterial Activity

Figure 10 illustrates the antibacterial activity of the gelatin/ZnO fibers against *E. coli* and *S. aureus* with and without UV light. The bacteria were determined by using the viable colony count method. Figure 11 represents photographs showing the antibacterial activity of gelatin/ZnO fibers against *S. aureus* and *E. coli*. Obviously, pure gelatin fibers (GZ0) have no toxic effect on the bacterial strains, and pure ZnO, GZ1 and GZ2 have excellent bacteriostatic effects. In addition, GZ2 containing a higher concentration of ZnO has stronger antibacterial activity than GZ1 containing a low concentration of ZnO. According to the reported literature [39–41], the reason for the antibacterial activity of gelatin/ZnO fibers is the superoxide radicals (·O2 −) produced by ZnO particles. The superoxide radicals can attack the bacterial cell wall and lead to cell wall leakage, resulting in the death of bacteria. In addition, under UV irradiation, ZnO particles can produce a large number of superoxide radicals. The obtained data (Figure 10) show that the antibacterial effect of gelatin/ZnO fibers irradiated by UV light is stronger than that of non-irradiated. This also proves the antibacterial mechanism of gelatin/ZnO fibers.

**Figure 10.** The antibacterial activity of the gelatin/ZnO fibers against (**a**) *Staphylococcus aureus* and (**b**) *Escherichia coli* with and without UV light. (\* represents *p* < 0.05, \*\* represents *p* < 0.01 and \*\*\* represents *p* < 0.001.).

**Figure 11.** The photographs showing the antibacterial activity of (**a**,**b**) negative control, (**c**,**d**) ZnO particles, (**e**,**f**) GZ0, (**g**,**h**) GZ1 and (**i**,**j**) GZ2 against *S. aureus* and *E. coli*, respectively.
