Assessing the Effect of Bile and Oxygen Availability on the Redox Status of Listeria monocytogenes Strain F2365

Although bile is a bactericidal agent able to disrupt membrane structure and cellular homeostasis, including the induction of oxidative stress, Listeria can tolerate bile and also utilize it as a signal to enhance infection and virulence. Preliminary findings showed that under anaerobic conditions, exposure to bile significantly lowered the amount of oxidative damage present in bile-resistant strain F2365 cells. Similarly, Listeria further elicits an adaptive immune response, wherein pre-exposure of the bacterium to stress during food processing or in the host prior to entry into the intestine increases bile tolerance. Based on these previous studies, we hypothesized that bile induces oxidative damage under aerobic, but not anaerobic conditions and that pre-exposure to oxidative stress can improve the oxidative stress response expressed from exposure to bile. The overall goal is to understand the effects of oxygen availability and bile on the redox state of F2365. To do so, oxidative stress marker GSH:GSSG ratio was measured in F2365 under aerobic and anaerobic conditions subsequent to one of four treatments: no treatment, 50 mM H2O2 only, 50 mM H2O2 followed by 1% bile, and only 1% bile. The results indicate a similar redox state of F2365 under both aerobic and anaerobic conditions. However, exposure to bile induced oxidative stress under aerobic conditions, but not under anaerobic conditions. Additionally, pre-exposure to hydrogen peroxide does not protect F2365 from bile-induced oxidative stress. Further research is needed to determine the normal-state GSH:GSSG ratio in Listeria and understand the different mechanisms Listeria uses to combat bile under aerobic and anaerobic conditions