title: The two-component system ScnRK of Streptococcus mutans affects hydrogen peroxide resistance and murine macrophage killing.
abstract: To survive macrophage killing is critical in the pathogenesis of viridians streptococci-induced infective endocarditis (IE). Streptococcus mutans, an opportunistic IE pathogen, generally does not survive well phagocytic killing in murine macrophage RAW 264.7 cells. A putative two-component system (TCS), ScnR/ScnK from S. mutans, was investigated to elucidate the mechanisms underlying bacteria-cellular interaction in this study. Both the wild-type and mutant strains were phagocytosed by RAW 264.7 cells at a comparable rate and an increased intracellular susceptibility during a 5 h incubation period was observed with the scnRK-null mutants. The amount of reactive oxygen species (ROS) in activated macrophages was reduced significantly after ingesting wild-type, but not scnRK-null mutant strains, suggesting that increased macrophage killing of these mutants is due to the impaired ability of S. mutans to counteract ROS. Additionally, both scnR- or scnRK-null mutants were more susceptible to hydrogen peroxide. Interestingly, scnRK expression was unaffected by hydrogen peroxide. These experimental results indicate that scnRK is important in counteracting oxidative stress in S. mutans, and decreased susceptibility to phagocytic killing is at least partly attributable to inhibition of intracellular ROS formation.
authors.affiliation: Department and Graduate Institute of Microbiology, College of Medicine, National Taiwan University, No. 1, Jen Ai Road Section 1, Taipei 10051, Taiwan, ROC.
authors.forename: Pei-Min
authors.initials: PM
authors.lastname: Chen
authors.forename: Heng-Chang
authors.initials: HC
authors.lastname: Chen
authors.forename: Chun-Ta
authors.initials: CT
authors.lastname: Ho
authors.forename: Chiau-Jing
authors.initials: CJ
authors.lastname: Jung
authors.forename: Huei-Ting
authors.initials: HT
authors.lastname: Lien
authors.forename: Jen-Yang
authors.initials: JY
authors.lastname: Chen
authors.forename: Jean-San
authors.initials: JS
authors.lastname: Chia
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000502:physiology*; D002460:Cell Line; D024881:Drug Resistance, Bacterial; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D051379:Mice; D009154:Mutation; D010587:Phagocytosis; D017382:Reactive Oxygen Species / Q000032:analysis / Q000378:metabolism; D013290:Streptococcal Infections / Q000276:immunology*; D013295:Streptococcus mutans / Q000737:chemistry* / Q000187:drug effects* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide