Department of Food Science, University of Pretoria, Lynwood Road, Pretoria 0002, South Africa.
Microbiol Res. 2010 Sep 20;165(7):546-56. doi: 10.1016/j.micres.2009.11.003. Epub 2009 Dec 14.
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.
耐酸型大肠杆菌 O157:H7 对不利应激的交叉保护作用由葡萄糖抑制的σ因子 RpoS 介导。然而，大肠杆菌 O157:H7 存在的许多食品系统较为复杂且含有葡萄糖。本研究旨在研究酸和乳过氧化物酶（LP）诱导基因对耐酸型大肠杆菌 O157:H7 对 LP 系统和乳酸（LA）在 Tryptone Soy Broth（TSB）中的交叉保护作用的贡献。将耐酸型和非耐酸型大肠杆菌 O157:H7 在 pH 4.0 和 5.0 的 TSB 中于 25°C 下用激活的 LP 和 LA 孵育 6 小时，随后检测酸和 LP 诱导基因的表达。耐酸型大肠杆菌 O157:H7 对激活的 LP 和 LA 表现出交叉保护作用。在 pH 4.0 时，测试的所有酸诱导基因均受到抑制，无论是否存在激活的 LP 系统。在 pH 7.4 时，gadA、ompC 和 ompF 在耐酸型细胞中被诱导。corA 在非耐酸型细胞中诱导，但在耐酸型细胞中被抑制。尽管在 pH 4.0 时酸诱导基因受到抑制，但耐酸型细胞的高抗性表明酸诱导基因的表达发生在酸适应期间，而不是实际的挑战期间。rpoS 的抑制表明 RpoS 独立系统有助于耐酸型大肠杆菌 O157:H7 的交叉保护。
