## 3 Results and Discussion
### Effects of Twist Coefficient on Antibacterial Rate of Functional Antibacterial Karnitted Fabrics  
Figures 7 and 8 show the colony count of _E. coli_ when two- and three-plied knitted fabrics are used. Figures 7a and 8a show the control groups that are knitted fabrics composed of two and three plies non-twisted zinc ion yarns, where the colony count is comparatively greater than the experimental group. In the meanwhile, a rise in the twist coefficient proportionally restrains the bacterial growth. This result is ascribed to a greater quantity of zinc ion yarns per unit area, suggesting that the antimicrobial effect is proportional to the twist coefficient.  
Figure 6: Antimicrobial efficacy of functional knitted fabrics before and after washing as related to the twist coefficient.  
Figure 9 shows the antibacterial rate of the control and experimental groups as related to the twist coefficient, and the antibacterial rate is computed using Equation (2). As for the knitted fabrics composed of two plies of zinc ion yarns, the antibacterial rate is only 15% for 2 Zn-1C-K, but it spikes to 81% for 2 Zn-5C-K. Similarly, as for the knitted fabrics composed of three plies of zinc ion yarns, the antibacterial rate is 32% for 3 Zn-1C-K and 85% for 3 Zn-5C-K. Namely, both a rise in zinc ion yarns and a rise in the twist coefficient have a positive influence on the antibacterial rate. Due to a greater total amount of nanometer zinc ion yarns per unit area, the resulting knitted fabrics demonstrate higher antibacterial performance.  
Figure 8: Colony count of functional antibacterial knitted fabrics made of 3-plied twisted yarns: (a) 3 Zn-0C-K, (b) 3 Zn-1C-K, (c) 3 Zn-2C-K, (d) 3 Zn-3C-K, (e) 3 Zn-4C-K, and (f) 3 Zn-5C-K.  
Figure 7: Colony count of functional antibacterial knitted fabrics made of 2-plied twisted yarns: (a) 2 Zn-0C-K, (b) 2 Zn-1C-K, (c) 2 Zn-2C-K, (d) 2 Zn-3C-K, (e) 2 Zn-4C-K, and (f) 2 Zn-5C-K.  
Nanometer zinc ions are able to kill and reduce the harmful effects of _E. coli_ because _E. coli_ is one type of Gram-negative bacteria. Despite a complex cell wall, _E. coli_ has a bacteria lipid bilayer as its outer membrane. The internal side of the lipid bilayer is composed of phospholipids that have a rather low strength. In addition, _E. coli_ carries negative electricity because of the presence of ionizing -COOH over its surface. In this case, nanometer zinc oxides dissociate antibacterial ions (Zn\({}^{2+}\)) that will be adsorbed by the surface of bacteria with the aim of the coulombic force, thereby impairing the cell wall of bacteria. Besides, zinc oxides also interfere with the synthesis of peptidoglycan, hampering cell walls from formation, while restraining the propagation and growth. Then, Zn\({}^{2+}\) can penetrate the cell walls, replacing the surface cations over cell membranes and interacting with sulfur- or nitrogen-containing functional groups from the interior of bacteria, such as protein and nucleic acid (i.e., -SH and -NH), thereby generating protein denaturation and immobilizing cell synthetase. In the meanwhile, the cell membranes are destroyed, which subsequently discharges cell contents, hampering synthesis and metabolism of metabolic enzymes, while restraining cells from propagating, growing, and developing normally [33; 34; 35; 36; 37].