XDH and bacterial infectious disease: Reactive oxygen species (ROS) such as the superoxide anion (O2•−), hydroxyl radical (•OH), and hydrogen peroxide (H2O2) are produced within cells through endogenous processes, including mitochondrial oxidative phosphorylation and the activity of various enzyme systems, including cyclooxygenase-2 (COX2), xanthine oxidase (XO), and NADPH oxidase (NOX), or they may derive from exogenous sources like ionizing radiation and bacterial infection [11,12].