Bhagwat Arvind A, Chan Lynn, Han Rachel, Tan Jasmine, Kothary Mahendra, Jean-Gilles Junia, Tall Ben D
Produce Quality and Safety Laboratory, Henry A. Wallace Beltsville Agricultural Research Center, Agricultural Research Service, USDA, Bldg. 002, 10300 Baltimore Avenue, Beltsville, MD 20705-2350, USA.
Infect Immun. 2005 Aug;73(8):4993-5003. doi: 10.1128/IAI.73.8.4993-5003.2005.
Acid resistance is perceived to be an important property of enterohemorrhagic Escherichia coli strains, enabling the organisms to survive passage through the acidic environment of the stomach so that they may colonize the mammalian gastrointestinal tract and cause disease. Accordingly, the organism has developed at least three genetically and physiologically distinct acid resistance systems which provide different levels of protection. The glutamate-dependent acid resistance (GDAR) system utilizes extracellular glutamate to protect cells during extreme acid challenges and is believed to provide the highest protection from stomach acidity. In this study, the GDAR system of 82 pathogenic E. coli isolates from 34 countries and 23 states within the United States was examined. Twenty-nine isolates were found to be defective in inducing GDAR under aerobic growth conditions, while five other isolates were defective in GDAR under aerobic, as well as fermentative, growth conditions. We introduced rpoS on a low-copy-number plasmid into 26 isolates and were able to restore GDAR in 20 acid-sensitive isolates under aerobic growth conditions. Four isolates were found to be defective in the newly discovered LuxR-like regulator GadE (formerly YhiE). Defects in other isolates could be due to a mutation(s) in a gene(s) with an as yet undefined role in acid resistance since GadE and/or RpoS could not restore acid resistance. These results show that in addition to mutant alleles of rpoS, mutations in gadE exist in natural populations of pathogenic E. coli. Such mutations most likely alter the infectivity of individual isolates and may play a significant role in determining the infective dose of enterohemorrhagic E. coli.
耐酸性被认为是肠出血性大肠杆菌菌株的一项重要特性，它使这些微生物能够在通过胃部的酸性环境时存活下来，从而得以在哺乳动物胃肠道中定殖并引发疾病。因此，该生物体已进化出至少三种在遗传和生理上截然不同的耐酸系统，这些系统提供不同程度的保护。依赖谷氨酸的耐酸（GDAR）系统利用细胞外谷氨酸在极端酸性挑战期间保护细胞，据信它能提供对胃酸的最高保护。在本研究中，对来自34个国家和美国23个州的82株致病性大肠杆菌分离株的GDAR系统进行了检测。发现29株分离株在有氧生长条件下诱导GDAR存在缺陷，而另外5株分离株在有氧以及发酵生长条件下的GDAR均存在缺陷。我们将低拷贝数质粒上的rpoS导入26株分离株，并且能够在有氧生长条件下使20株酸敏感分离株恢复GDAR。发现4株分离株在新发现的类LuxR调节因子GadE（以前称为YhiE）中存在缺陷。其他分离株的缺陷可能是由于在耐酸中作用尚未明确的基因发生了突变，因为GadE和/或RpoS无法恢复耐酸性。这些结果表明，除了rpoS的突变等位基因外，致病性大肠杆菌的自然群体中还存在gadE的突变。此类突变很可能会改变单个分离株的感染性，并且可能在确定肠出血性大肠杆菌的感染剂量方面发挥重要作用。
