title: Relative gene expression in acid-adapted Escherichia coli O157:H7 during lactoperoxidase and lactic acid challenge in Tryptone Soy Broth.
abstract: Cross-protection of acid-adapted Escherichia coli O157:H7 against inimical stresses is mediated by the glucose-repressed sigma factor RpoS. However, many food systems in which E. coli O157:H7 occurs are complex and contain glucose. This study was aimed at investigating the contribution of acid and lactoperoxidase (LP)-inducible genes to cross-protection of E. coli O157:H7 against LP system and lactic acid (LA) in Tryptone Soy Broth (TSB). Acid-adapted and non-adapted E. coli O157:H7 were challenged to activated LP and LA at pH 4.0 and 5.0 in TSB for 6h at 25°C followed by expression of acid and LP-inducible genes. Acid-adapted E. coli showed cross-protection against activated LP and LA. All the acid-inducible genes tested were repressed at pH 4.0 with or without activated LP system. At pH 7.4, gadA, ompC and ompF were induced in acid-adapted cells. Induction of corA occurred in non-adapted cells but was repressed in acid-adapted cells. Although acid-inducible genes were repressed at pH 4.0, high resistance of acid-adapted cells indicates that expression of acid-inducible genes occurred during acid adaptation and not the actual challenge. Repression of rpoS indicates that RpoS-independent systems contribute to cross-protection in acid-adapted E. coli O157:H7.
authors.affiliation: Department of Food Science, University of Pretoria, Lynwood Road, Pretoria 0002, South Africa.
authors.forename: Angela A
authors.initials: AA
authors.lastname: Parry-Hanson
authors.forename: Piet J
authors.initials: PJ
authors.lastname: Jooste
authors.forename: Elna M
authors.initials: EM
authors.lastname: Buys
mesh_terms: D000143:Acids / Q000378:metabolism; D000222:Adaptation, Physiological; D003470:Culture Media / Q000378:metabolism; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D005520:Food Preservatives / Q000494:pharmacology*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D019344:Lactic Acid / Q000494:pharmacology*; D007784:Lactoperoxidase / Q000494:pharmacology*; D050296:Microbial Viability / Q000187:drug effects; D010461:Peptones / Q000378:metabolism*
chemical_list: D000143:Acids; D003470:Culture Media; D029968:Escherichia coli Proteins; D005520:Food Preservatives; D010461:Peptones; D019344:Lactic Acid; C001830:tryptones; D007784:Lactoperoxidase