Role of manganese-containing superoxide dismutase in oxidative stress and virulence of Streptococcus pneumoniae

Streptococcus pneumoniae was shown to contain two types of superoxide dismu tase, MnSOD and FeSOD, Levels of MnSOD increased during growth in an aerobi c environment. The sodA gene, encoding MnSOD, of virulent S. pneumoniae typ e 2 strain D39 was inactivated to give mutant D39HY1. Aerobically, D39HY1 h ad a lower growth rate than the wild type and exhibited susceptibility to t he redox-active compound paraquat, but anaerobic growth of D39HY1 was ident ical to that of the wild type. Virulence studies showed that the median sur vival time of mice infected intranasally with D39HY1 was significantly long er than that of mice infected with the wild-type pneumococcus. In contrast to the wild type, D39HY1 did not multiply in lungs during the first 24 h bu t thereafter grew at the same rate as the wild type. Appearance in the bloo dstream was also delayed, but growth in the blood was unimpaired by the sod A mutation. The pattern of inflammation in lungs infected with D39HY1 diffe red from that in wild-type-infected mice. After infection with D39HY1, neut rophils were densely packed around bronchioles, in contrast to the wild-typ e infection, where neutrophils were more diffusely localized.