## 4 Discussion
One of the factors behind cell death is the disruption of the mitochondrial function. Strong indications of apoptosis, the loss of the mitochondrial potential, and an increase in ROS generation were observed in the cells exposed to ZnO particulate matter. However, when the cells were exposed to a similar quantity of a soluble Zn salt, these signs were not present. There was a statistically significant increase in the potency per unit mass with the smaller particles compared with the larger particles, even though both ZnO samples produced similar toxicity mechanisms [73]. Nevertheless, there are concerns about the toxicity of nanoparticles under 100 nm in comparison with larger particles of the same substance [73]. However, zinc oxide nanoparticles selectively harm bacteria while having little effect on human and animal tissues. Additionally, zinc is recognized as an essential trace element for the physiological and biochemical processes in humans and animals. Therefore, the Food and Drug Administration has approved the use of zinc as a food additive [12; 74]. According to our results (Table 2), the studied bacteria and fungi had significantly varied interactions toward the synthesized ZnO nanoparticles as antimicrobial agents, with varied ZI marginal means. _Pseudomonas aeruginosa_ (Gram-negative bacterium) was the microbe that was the least affected by the ZnO nanoparticles, compared with _Staphylococcus aureus_ and the other tested fungi, which suggests that it had a resistance tendency towards ZnO nanoparticles. ZnO NPs have the capability of inhibiting the growth of both Gram-positive and Gram-negative bacteria, as well as that of fungi. The sensitivity of the bacteria determines the strength of the antimicrobial impact [75]. A thick film of peptidoglycan (20-80 nm) makes up the cell wall of Gram-positive bacteria, acting as a physical barrier to safeguard the surroundings of the cell. Teichoic and lipoteichoic acids, as well as surface proteins, are polymers that are fixed by this thick layer of peptidoglycan. Gram-negative bacteria have highly complex cell walls [68; 76]. According to [PERSON] and colleagues [77], Gram-positive bacteria are more vulnerable to ZnO-nanoparticle attacks than Gram-negative bacteria. The antibacterial attributes of zinc oxide nanoparticles have been shown to be directly proportional to their concentration and particle surface area [78]. However, ZnO nanoparticles have the potential to alter the environment around bacteria by creating ROS or by modifying the cell wall of the microbe as a result of the electrostatic binding of the ZnO nanoparticles to the cell surface, which can lead to cellular destruction [79; 80]. Because it immediately lowers the amount of oxygen in the water, some bacteria have cytochrome oxidase, which can interfere with the antibacterial effects of ZnO nanoparticles. _P. aeruginosa_ has strong drug resistance because it produces both catalase and cytochrome oxidase, which enable bacteria to scavenge hydrogen peroxide radicals [68; 81]. Because of their unique characteristics, such as their crystallinity, porosity, and particle size and shape, ZnO NPs are capable of inhibiting a wide variety of pathogens, including _Escherichia coli_, _Staphylococcus aureus_, _Pseudomonas aeruginosa_, _Bacillus subtilis_, etc. [82; 83]. Reactiveoxygen species (ROS)-based photocatalytic antimicrobial interactions under ultraviolet (UV) and visible light irradiation are also enhanced by the intra- and interparticle pores of ZnO NPs [3]. A cell membrane's ability to adsorb ZnO nanoparticles for antibacterial activities is also facilitated by their high specific surface areas [17]. Research authors [84; 85] have conclusively reported that ZnO NPs exhibit antibacterial activity, depending on the concentration and surface area, because more H\({}_{2}\)O\({}_{2}\) radicals can be created on the surfaces of ZnO nanoparticles. Increases in the nanoparticle concentration and surface area can lead to increased antibacterial activity.