55 × 107 4.35 × 107 4.0 × 107 6.25 × 106 2.0 × 105 Zn (NO3)2 9.65 × 107 9.15 × 107 8.9 × 107 8.3 × 107 1.01 × 107 2.6 × 105 6.0 × 102 ZnCl2   7.35 × 104 5.6 × 104 2.0 × 104 3.5 × 103 1.9 × 103 1.7 × 102 34 The initial bacterial colony count is 9.9 × 105 CFU/mL. SEM characterization of E. coli and S. aureus cells Figures 6 and 7 show the SEM images of the bacterium before and after treatment with the titanium-doped ZnO powders. In control samples, the E. coli cell walls are rough and intact (Figure 6a). However, after being treated with the titanium-doped ZnO

powders, the morphologies of E. coli cells show changes in varying Nutlin-3a chemical structure degrees. Figure 6b,c shows that the E. coli cells are damaged slightly after treatment with the ZnO powders prepared from zinc acetate and zinc sulfate. By comparison, the E. coli cells

are damaged seriously when treated by powders synthesized from zinc nitrate (Figure 6d), and the E. coli cells are damaged most seriously being treated by the powders Wortmannin synthesized from zinc chloride (Figure 6e). As shown in Figure 7a, the S. aureus cells exhibit well-preserved cell walls. After treatment with titanium-doped ZnO powders synthesized from zinc acetate and zinc sulfate, the crinkling of the S. aureus cell walls appeared (Figure 7b,c). However, after being treated with the powders synthesized from zinc nitrate, the S. aureus cell walls are damaged into honeycomb (Figure 7d). It is obvious that the effect of the powders synthesized from zinc chloride is the most drastic, and S. aureus cells are ruptured (Figure 7e). Figure 6 SEM images of E. coli cells before and after treatment by titanium-doped ZnO powders. (a) Control, (b) zinc acetate, (c) zinc sulfate, (d) zinc nitrate, and (e) zinc chloride. Figure 7 SEM images of S. aureus cells before and after treatment by titanium-doped ZnO powders. (a) Control, (b) zinc acetate, (c) zinc sulfate, (d) zinc nitrate, and (e) zinc chloride. From what

is mentioned above, we can reach the conclusion that the extent of damage to E. coli and S. aureus cells is positively related to the antibacterial properties of titanium-doped ZnO powders (Tables 1 and 2). Moreover, many powders are attached to the bacterial cells’ surfaces, and the energy-dispersive spectrometer results (Additional file 1) demonstrate that they are titanium-doped ZnO particles (yellow circles in Figures 6 and 7 correspond Ergoloid to the EDS spectra in Additional file 1 in sequence). The electrical conductivity of bacterial suspension before and after treatment Figure 8 shows the electrical conductance changing trend of the E. coli and S. aureus suspension treated with titanium-doped ZnO powders synthesized from different zinc salts with different times. The results show that the electrical conductance of the control bacterial suspension is nearly unchanged. However, the electrical conductance of the bacterial suspension increases obviously, which are treated with titanium-doped ZnO powders.