title: Characterization of enterohemorrhagic Escherichia coli strains based on acid resistance phenotypes.
abstract: 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.
authors.affiliation: 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. bhagwata@ba.ars.usda.gov
authors.forename: Arvind A
authors.initials: AA
authors.lastname: Bhagwat
authors.forename: Lynn
authors.initials: L
authors.lastname: Chan
authors.forename: Rachel
authors.initials: R
authors.lastname: Han
authors.forename: Jasmine
authors.initials: J
authors.lastname: Tan
authors.forename: Mahendra
authors.initials: M
authors.lastname: Kothary
authors.forename: Junia
authors.initials: J
authors.lastname: Jean-Gilles
authors.forename: Ben D
authors.initials: BD
authors.lastname: Tall
mesh_terms: D001422:Bacterial Adhesion / Q000502:physiology; D001426:Bacterial Proteins / Q000378:metabolism; D018938:Caco-2 Cells; D003470:Culture Media; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism; D020869:Gene Expression Profiling; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D012808:Sigma Factor / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000172:deficiency / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D029968:Escherichia coli Proteins; C479562:GadE protein, E coli; D012808:Sigma Factor; D014157:Transcription Factors; C069567:sigma factor KatF protein, Bacteria; D018698:Glutamic Acid; D005968:Glutamate Decarboxylase