Oxidative stress response in Shigella & nonpathogenic gut bacteria

Abstract

The effect of oxidative stress in the form of exogenous H₂O₂ on the survival of four species of Shigella and two nonpathogenic Gram negative gut bacteria and the role of catalase as an antioxidant enzyme, neutralizing the effect of H₂O₂ were examined. A significant decrease in the number of colony forming units (CFUs) after exposure to exogenous H₂O₂ (122 ± 37), compared to control bacteria (218 ± 63, P < 0.001) was observed. There was an induction of catalase activity after exposure to exogenous H₂O₂ and the specific activity of catalase in H₂O₂ exposed bacteria was significantly increased (2.88 ± 1.25), compared to control bacteria (1.5 ± 0.44; P < 0.05). A direct correlation was observed between the decrease in bacterial counts and increase in catalase activity after exposure of H₂O₂ (regression coefficient (0.56). Gut bacteria appear to be susceptible to oxidative stress and inducible catalase activity may form an important part of the antioxidant defence mechanism against oxidative stress.