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，被认为是居住在大肠中的严格厌氧菌的教科书例子。脆弱梭菌是结肠的正常居民，但艰难梭菌通常出现在正常微生物群因抗生素治疗而受损的人群中。脆弱芽孢杆菌是一种机会致病菌，主要与渗漏进入腹腔形成脓肿而从肠道逃逸有关。另一方面，艰难梭菌是抗生素相关性腹泻和假膜性结肠炎的主要原因。鉴于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，脆弱杆菌和艰难梭菌的突变体可以在氧气存在（高达2%）的情况下生长，并且可以在更高的氧气水平下存活。这些突变体中的许多都有氧（促氧）零突变，这种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，许多来自脓肿的脆弱芽孢杆菌的临床分离株可以在1.5%的氧气中生长，并且也有oxeA突变。本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其有氧生长的基因？我们的工作假设是，oxe基因的野生型产物促进了厌氧结肠中的生长或存活，而oxe突变则增强了动物宿主的某些发病机制。为了验证这一假设，我们将比较易碎芽孢杆菌和艰难梭菌野生型和oxe突变株在疾病动物模型中的定植、毒力和传播。此外，我们将寻求揭示在低氧水平下，氧基因产物阻止生存和生长的生化机制。结果有望揭示厌氧生长的一个新颖和令人惊讶的方面。

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.