Purpose: The purpose of this study was to investigate the role of oxidative stress in the survival of C. jejuni under oxygen-rich conditions.
Methods: The effect of oxidative stress on aerotolerance was investigated in C. jejuni by using three mutants defective in key genes of oxidative stress defense, including ahpC, katA, and sodB. We measured the levels of viability and accumulation of reactive oxygen species (ROS) under aerobic conditions, and observed morphological changes with fluorescence microscopy.
Results: All the three mutants exhibited reduced viability under aerobic conditions compared to the wild type (WT), and the ahpC mutant showed most significant viability reductions. The levels of lipid peroxidation and protein oxidation were significantly increased in the mutants compared to WT. Under aerobic conditions, the ahpC and katA mutants developed coccoid forms by aeration, whereas the sodB mutant established elongated cellular morphology. Higher levels of ROS were accumulated in C. jejuni under aerobic conditions than microaerobic conditions, and supplementation of culture media with an antioxidant reduced the level of ROS accumulation and also increased C. jejuni viability under aerobic conditions. Compared to microaerobic conditions, interestingly, aerobic culture substantially induced the formation of coccoid cells, and antioxidant treatment reduced the emergence of coccoid cells, possibly viable-but-non-culturable cell (VBNC), under aerobic conditions. The ATP concentrations and PMA-qPCR analysis supported that oxidative stress is a factor that induces the development of a VBNC state in C. jejuni.
Significance: These findings in this study clearly demonstrated that oxidative stress resistance plays an important role in the survival and bacterial morphology of C. jejuni under aerobic conditions.