Absence of catalase reduces long-term survival of Helicobacter pylori in macrophage phagosomes

Background. Some Helicobacter pylori strains can survive within macrophage phagosomes for up to 24 hours. The factors that play a role in this survival remain ill-defined. Therefore, the contribution of catalase in mediating the survival of H. pylori following phagocytosis was investigated in vitro. Methods. An isogenic, catalase-deficient strain of H. pylori was generated and tested for sensitivity to hydrogen peroxide and susceptibility to macrophage-mediated killing. Results. The isogenic, catalase-deficient strain of H. pylori was effectively killed by hydrogen peroxide within 3 minutes compared to wild-type H. pylori which maintained 100% survival up to 21 minutes. The catalase-deficient mutant was also significantly more susceptible to macrophage-mediated killing than the parent strain, even when the ratio of bacteria to macrophage was increased. Conclusion. These results indicate that although some strains of H. pylori are capable of survival within the macrophage phagosome, survival is dependent on virulence factors such as catalase for evasion of innate host defense.