## 3 Results
### Sterilization of Microorganism in Water-Soluble Cutting Fluids  
The experiment was conducted using a water-based cutting fluid for 6 to 12 months. The bacterial concentration after 48 h of incubation was 1.14 \(\times\) 10\({}^{6}\) CFU/mL, and six morphologically different bacteria were isolated from the water-soluble cutting fluid (Figure 5). Six morphologically different bacteria were identified; a list of them is presented in Table 1 [26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48]. Among these, _Achromobacter_, _Citrobacter_, _Pseudomonas_, and _Staphylococcus_ were the major genera identified in the water-soluble cutting fluid. Among the isolated bacteria, _Achromobacter xylosoxidants_ has been isolated from hospitals, homes, and water, has been reported to produce foul odors, and is infectious to humans [26; 27; 28; 29; 30], whereas _Citrobacter farmeri_ has been reported to cause illness in humans and is also known to produce foul odors [31; 32; 33]. Strains of _Pseudomonas chemquisis_ have been found in humans (disease), animals, waste cooking oil, and landfills and have been reported as odor-causing bacteria, similar to other bacteria. However, unlike other bacteria, _P. chengduensis_ has not been reported in human disease cases [34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44]. The last isolate, _Staphylococcus warneri_, has been found in the environment and animals and has been reported as an odor-causing bacterium in disease reports [45; 46; 47; 48]. Figure 6a shows the bacterial sterilization of the cutting fluid samples using the ozone treatment. It can be seen that the plasma-generated ozone treatment sharply reduced microbial growth by 40 min, and more than 99% were killed after 60 min of treatment. Figure 6b shows the morphology of the cultured bacteria as a function of the ozonation time, with small differences between 40 and 100 min. The bacteria tested in Figure 6 are a mixture of the six types.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Species No.** & **Species Name** & \multicolumn{2}{c}{**Properties**} & **Reference** \\ \cline{3-5}  & & **Location** & **Odor** & **Human Infection** \\ \hline A & _Achromobacter xylosoxidants_ & Human, environment & \(\bigcirc\) & [26; 27; 28; 29; 30] \\ B & _Citrobacter farmeri_ & Human, environment & \(\bigcirc\) & [31; 32; 33] \\ C & _Pseudomonas aeruginosa_ & Human, animal, environment & \(\bigcirc\) & [34; 35; 36; 37; 38; 39; 40] \\ D & _P. chengduensis_ & Landfill leachate & \(\bigcirc\) & X & [41] \\ E & _P. olovorans_ & Human, environment & \(\bigcirc\) & [42; 43; 44] \\ F & _Staphylococcus warneri_ & Human, animal & \(\bigcirc\) & [45; 46; 47; 48] \\ \hline \end{tabular}
\end{table}
Table 1: List of bacteria isolated and identified from the water-based cutting fluids and their properties.  
Figure 5: Morphology of bacteria isolated from water-based cutting fluids. (**a**) Achromobacter xylosoxidants; (**b**) Citrobacter farmeri; (**c**) Pseudomonas aeruginosa; (**d**) Pseudomonas; (**e**) Pseudomonas oleovorans; (**f**) Staphylococcus warneri.  
Figure 7 shows a schematic of the process of bacterial death upon treatment with ozone. Ozone binds to bacterial cell membranes composed of proteins, and an oxidation process occurs. In this process, one molecule of oxygen weakens cell membrane protein binding and destroys the bacterial cell membrane so that organs related to growth and proliferation inside the cell are eluted and the bacteria die [49; 50].  
Figure 6: The sterilization of bacteria from the sample cutting fluid according to the ozone treatment. (**a**) Plot showing the death of bacteria at different treatment times (\(n=3\)). (**b**) Bacteria image on Petri dish corresponding to (**a**).  
Figure 7: Schematic diagram of bacterial death by ozone treatment.