Role of reactive oxygen species in the correlation between host and microbes

Free radicals have the nature of unpaired electrons in their outer orbital that render them as highly reactive species. Specifically, aerobic cells produce hydroxyl radicals, hydrogen peroxide, and superoxide anions known as reactive oxygen species (ROS). Host immune systems generate ROS as defense mechanisms to clear pathogens. It is plausible that microbes can thrive in oxidative environments by decreasing host responses mediated by ROS during infection or inducing several genes encoding antioxidant enzymes. However, ROS at high concentrations have an adverse effect on any cellular components. Based on the significant impact on antimicrobial actions, antimicrobials efficiently kill bacteria by inducing ROS and targeting production of ROS, thus strengthening anti-microbial activity. Therefore, the balance of ROS needs to be investigated to control microbial infections and associated diseases. This chapter is focused on the role of ROS between host and pathogens.