Journal
MICROBIOLOGICAL RESEARCH
Volume 165, Issue 7, Pages 546-556Publisher
ELSEVIER GMBH
DOI: 10.1016/j.micres.2009.11.003
Keywords
Cross-protection; Escherichia coli O157:H7; Lactoperoxidase; Acid-adaptation and real-time PCR
Categories
Funding
- National Research Fund
- Third World Organization for Women in Science
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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 0157: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 0157:H7 against LP system and lactic acid (LA) in Tryptone Soy Broth (TSB). Acid-adapted and non-adapted E. coli 0157:H7 were challenged to activated LP and LA at pH 4.0 and 5.0 in TSB for 6 h at 25 degrees 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 0157:H7. (C) 2009 Elsevier GmbH. All rights reserved.
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