Shiga Toxin Encoding Phage and Intestinal E.coli

描述（由申请人提供）：产志贺毒素的大肠杆菌，包括O157:H7，是新兴的重要病原体。细菌定植与肠道紊乱有关；然而，严重的、可能致命的血性腹泻（出血性结肠炎）和导致溶血性尿毒症综合征（HUS）的肾脏破坏是由一种细菌毒素——志贺毒素引起的。志贺毒素的基因是由一个温和的噬菌体在晚期基因操纵子中编码的。当噬菌体裂解周期被诱导时，志贺毒素与产生病毒颗粒和细菌裂解所需的基因一起表达。噬菌体介导的细菌裂解是毒素分泌所必需的。致病性O157:H7感染过程中产生的病毒颗粒可感染非致病性肠道大肠杆菌。当这种情况发生时，以前无害的大肠杆菌将产生志贺毒素并放大致病过程。我们的初步数据表明，肠道菌群产生的志贺毒素可能是大量的，并且在肠道菌群可能被志贺毒素噬菌体感染的个体中更有可能发生严重的，可能危及生命的疾病。相反，肠道菌群对志贺毒素噬菌体具有抗性的个体将免受严重疾病的侵害。

DESCRIPTION (provided by applicant): Shiga toxin-producing Escherichia coli, including O157:H7, are emerging pathogens of major importance. Bacterial colonization is associated with intestinal disturbances; however, the severe, potentially fatal symptoms of bloody diarrhea (hemorrhagic colitis) and destruction of the kidney leading to hemolytic uremic syndrome (HUS) are due to a bacterial toxin, Shiga toxin. The genes for Shiga toxin are encoded by a temperate bacteriophage in the late gene operon. Shiga toxin is expressed when the phage lytic cycle is induced, along with the genes necessary for production of viral particles and bacterial lysis. Phage-mediated bacterial lysis is necessary for toxin secretion. The viral particles produced during infection with the pathogenic O157:H7 can infect the nonpathogenic intestinal E. coli. When this occurs, the previously harmless E. coli will produce Shiga toxin and amplify the pathogenic process. Our preliminary data suggest that the Shiga toxin production by intestinal flora can be substantial and that severe, possibly life-threatening disease is more likely to occur in individuals whose intestinal flora can be infected by the Shiga toxin phage. In contrast, individuals with intestinal flora that are resistant to the Shiga toxin phage will be protected from severe disease. Currently, it is difficult to prevent disease by E. coli O157:H7 since the infectious dose is very low, and antibiotic treatment, instead of being beneficial, can enhance progression to fatal disease. We propose to develop methods to convert the intestinal flora to phage-resistance as a therapeutic approach to controlling disease caused by Shiga toxin-producing pathogens. This is especially important since there is no treatment, other than supportive care, once disease has developed. The specific aims of this application are to: 1) Characterize Shiga toxin production by clinical isolates of O157:H7 in the presence of susceptible or resistant human intestinal E. coli; and 2) Develop methods to convert intestinal flora to phage resistance using a mouse model of disease.