Aerobic Growth of Anaerobic Pathogens

描述（由申请人提供）：两种非常不同的细菌病原体，革兰氏阴性脆弱拟杆菌和革兰氏阳性艰难梭菌，被认为是大肠严格厌氧菌的教科书示例。B。fragilis是结肠的正常居民，而C.艰难梭菌通常存在于正常微生物群因抗生素治疗而受损的人群中。B。脆弱菌是一种机会致病菌，主要与由于渗漏进入腹膜腔并在腹膜腔中形成脓肿而从肠中逃逸有关。C.另一方面，艰难梭菌是腹泻相关性腹泻和伪膜性结肠炎的主要原因。考虑到这些细菌的正常栖息地是大肠的厌氧环境，值得注意的是，我们的初步结果表明，B. fragilis和C.艰难梭菌出现，可以在氧气（高达2%）的存在下生长，并可以在暴露于更高的氧气水平下存活。这些突变体中的许多都有oxe（氧使能）无效突变，这些突变存在于一个名为oxeA的基因中，该基因在两个非常不同的物种中是保守的。此外，许多临床分离的B。来源于酵母的fragilis可以在1.5%的氧气中生长，并且也具有oxeA突变。这项申请试图通过解决一个基本的生物学问题来解释这些意想不到的发现：为什么厌氧病原体通常表达其产物阻止它们有氧生长的基因？我们的工作假设是oxe基因的野生型产物促进厌氧结肠中的生长或存活，而oxe突变增强动物宿主中发病机制的某些方面。为了验证这一假设，我们将比较B的定殖、毒力和传播。fragilis和C.艰难梭菌野生型和oxe突变株在疾病动物模型中的应用。此外，我们将寻求揭示oxe基因产物阻止在低氧水平下生存和生长的生化机制。这些结果有望揭示厌氧生长的一个新的和令人惊讶的方面。

DESCRIPTION (provided by applicant): Two very different bacterial pathogens, the Gram-negative Bacteroides fragilis and the Gram-positive Clostridium difficile, have been considered as textbook examples of strict anaerobes that inhabit the large intestine. B. fragilis is a normal inhabitant of the colon, but C. difficile is usually found in people whose normal microbiota has been compromised by antibiotic treatment. B. fragilis is an opportunistic pathogen mainly associated with escape from the intestine due to leakage into and formation of abscesses in the peritoneal cavity. C. difficile, on the other hand, is the primary cause of antibiotic-associated diarrhea and pseudomembranous colitis. Given that the normal habitat for these bacteria is the anaerobic environment of the large intestine, it is remarkable that our preliminary results have shown that mutants of B. fragilis and C. difficile arise that can grow in the presence of oxygen (up to 2%) and can survive exposure to even higher oxygen levels. Many of these mutants have oxe (oxygen-enabling) null mutations that lie in a gene called oxeA that is conserved in the two otherwise very dissimilar species. Moreover, many clinical isolates of B. fragilis derived from abscesses can grow in 1.5% oxygen and have oxeA mutations as well. This application seeks to explain these unexpected findings by addressing a fundamental biological question: Why do anaerobic pathogens normally express genes whose products prevent them from growing aerobically? Our working hypothesis is that the wild-type product(s) of the oxe genes promote growth or survival in the anaerobic colon whereas the oxe mutations enhance some aspects of pathogenesis in animal hosts. To test this hypothesis we will compare the colonization, virulence and transmission of B. fragilis and C. difficile wild-type and oxe mutant strains in animal models of disease. In addition, we will seek to uncover the biochemical mechanisms by which the oxe gene products prevent survival and growth in low levels of oxygen. The results are expected to reveal a novel and surprising aspect of anaerobic growth.