Group A Streptococcus Responses to Oxidative Stress

Group A Streptococcus (GAS) employs multiple defense strategies to resist killing by reactive oxygen species (ROS) formed either by reduction of atmospheric oxygen or by phagocytes upon activation of the host inflammatory response. These defenses seem to be coordinated, at least in part, by the peroxide response transcriptional regulator, PerR. Our recent findings demonstrate a key role for PerR-regulated gene expression in counteracting the phagocyte oxidative burst and a critical contribution to GAS adaptation in the host during pharyngeal colonization. Further evidence indicates that multiple loci are under PerR control in GAS, including alkyl hydroperoxidase, metal transport, and sugar uptake and utilization loci. <P>To date, however, the GAS genes regulated in response to oxidative stress, including those regulated by PerR, have not been defined. Our data also show that perR is co-transcribed from an operon encompassing four additional genes of which three are predicted to be involved in GAS stress responses. Of these, polA.1 encodes DNA polymerase I, which has been implicated in DNA damage repair in several bacterial species, as well as in virulence of Salmonella typhimurium. Transcriptional linkage of polA.1 with perR raises the possibility that PolA.1 contributes to GAS virulence by repairing DNA damage inflicted by the oxidative burst of host phagocytes, in what may be both a novel and a conserved genetic and functional association with PerR in pathogenic streptococci. <P>The goals of this project are to characterize GAS adaptive responses coordinated by PerR under oxidative stress, and begin to examine the role, if any, of the perR operon gene products in GAS responses to oxidative stress during infection. <P>The specific aims are: 1) Characterize PerR-dependent and independent GAS responses to ROS generated by human neutrophils; 2) Determine whether the perR-linked DNA polymerase I (polA.1) plays a role in GAS oxidative stress responses and virulence. <P>Comparison of global responses to hydrogen peroxide (H2O2) or to H2O2 combined with human neutrophil granule contents in wild type versus perR mutant bacteria will define PerR-dependent and independent GAS responses to ROS generated by NADPH oxidase and myeloperoxidase as well as other effector molecules of human neutrophil granules, and will exemplify bacterial responses elicited by the phagocyte oxidative burst during infection. Moreover, construction and testing of a polA.1 mutant against oxidative stress challenge in vitro, or against phagocytosis by human leukocytes, will assess the contribution of PolA.1 to GAS in vivo fitness and virulence, and will reveal any putative functional relationship of this locus with PerR adaptive responses to oxidative stress. <P>The data obtained will further our understanding of the GAS adaptation mechanism(s) and survival in the host, and may uncover candidate target molecules and/or pathways for future investigations towards vaccine development or disease treatment. <P>PUBLIC HEALTH RELEVANCE: Group A Streptococcus (Streptococcus pyogenes or GAS) is the leading cause of human bacterial pharyngitis, an infection state commonly referred to as 'strep throat', but it is also implicated in skin and soft tissue infections, as well as life threatening invasive disease and the post-streptococcal autoimmune conditions of acute rheumatic fever and heart disease. A GAS vaccine is currently lacking but penicillin is usually effective against infection to prevent serious complications. However, when treatment fails or infection goes untreated, initial infection may progress to serious disease or trigger post-streptococcal autoimmune disease. <P>The proposed work aiming to characterize the contribution of the peroxide response regulator (PerR) to GAS survival in the human host will improve current understanding of the GAS strategies to avoid killing by phagocytic cells of the immune system, and may uncover target molecules and/or pathways for the development of new antibacterial targets or a GAS vaccine.