Growth and Colonization of the Intestine by E. coli

描述（由申请人提供）：大肠杆菌是哺乳动物胃肠道中主要的兼性厌氧菌。然而，大肠杆菌如何在哺乳动物宿主体内定居的本质尚不清楚。根据营养生态位假说，肠道中众多的生态位是由营养物质的可用性决定的，物种通过竞争一种或几种限制性营养物质而共存。这一假设表明，共生大肠杆菌菌株可能作为抵御肠道大肠杆菌病原体的第一道防线，但尚未就此进行过测试。在这一竞争性更新应用中，我们建议通过测试粘液来源的营养物质为竞争的大肠杆菌共生菌株和致病菌株提供营养壁龛的假设，来扩展我们对肠道定植的营养基础的研究。第一个具体目标是验证不同的大肠杆菌共生和致病菌株优先使用不同的营养物质在小鼠肠道定植的假设。进展报告中描述的工作表明，不同的大肠杆菌菌株使用不同的营养物质进行定植。对于代表大肠杆菌四个系统发育群的菌株，在定植开始和维持阶段的特定营养需求将通过使用为当前资助的项目开发的策略来确定，即，在模拟小鼠肠道的条件下，在DNA阵列上诱导的基因将被敲除，突变体将与其野生型亲本竞争测试，以确定其相对适合定植。第二个具体目标将检验这样一个假设，即优先利用不同的营养物质和/或切换到替代营养的能力是代表四个系统发育群的大肠杆菌菌株共定植的基础。推论假设也将得到验证，即对相同营养物质的直接竞争导致其中一种菌株的定植适应性降低。这些研究可能有助于解释人类对大肠杆菌病原体感染的易感性差异。

DESCRIPTION (provided by applicant): Escherichia coli is the predominant facultative anaerobe in the gastrointestinal tracts of mammals. Yet the essence of how E. coli colonizes its mammalian hosts is not understood. According to the nutrient-niche hypothesis, the numerous ecological niches in the intestine are defined by nutrient availability and species coexist by competing for one or a few limiting nutrients. This hypothesis suggests that commensal E. coli strains might act as a first line of defense against enteric E. coli pathogens, but it has not been tested in that light. In this competing renewal application, we propose to extend our investigation of the nutritional basis for intestinal colonization by testing the hypothesis that mucus-derived nutrients provide nutritional niches occupied by competing E. coli commensal and pathogenic strains. The first specific aim will test the hypothesis that different E. coli commensal and pathogenic strains preferentially use different nutrients for colonization of the mouse intestine. Work described in the progress report suggests that different E. coli strains use different nutrients for colonization. For strains representing the four phylogenetic groups of E. coli, the specific nutrient requirements during the initiation and maintenance stages of colonization will be determined by using strategies developed for the currently funded project, i.e., genes induced on DNA arrays under conditions designed to mimic the mouse intestine will be knocked out and the mutants tested in competition with their wildtype parent to determine their relative fitness for colonization. The second specific aim will test the hypothesis that preferential utilization of different nutrients and/or the ability to switch to alternative nutrition is the basis for co-colonization of E. coli strains representing each of the four phylogenetic groups. The corollary hypothesis will also be tested, that direct competition for the same nutrient leads to decreased fitness for colonization of one of the strains. These studies may help explain differences in human susceptibility to infection by E. coli pathogens.