Molecular Characterization of Foodborne Pathogens Research Unit, Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, PA, USA.
Microbiology (Reading). 2012 Sep;158(Pt 9):2225-2234. doi: 10.1099/mic.0.059535-0. Epub 2012 Jun 14.
In many Escherichia coli serotype O157 : H7 strains, defences against peroxide damage include the peroxiredoxin AhpCF and three catalases: KatG (catalase/peroxidase), KatE (catalase) and the plasmid-encoded KatP (catalase/peroxidase). AhpC and KatG basal expression is maintained by RpoS, and AhpC, KatG and KatP are all induced by OxyR/σ(70) in exponential phase. KatE is regulated by RpoS during stationary growth and is independent of OxyR. In a previous study we used mutant strains of ATCC 43895 (EDL933) with deletions of katG, ahpC, katE and katP in all possible combinations to characterize peroxide resistance during both exponential and 18-24 h growth in Luria-Bertani broth at 37 °C. In this study, we used triple deletion strains that isolated each catalase/peroxidase gene to investigate their role in the peroxide resistance of biofilm-forming variant 43895OR in 48 and 72 h biofilms. We also used quantitative real-time reverse transcriptase PCR and translational lacZ fusions to study gene expression. Peroxide resistance was greater (P<0.05) in biofilm cells than in planktonic cells, and full resistance required rpoS but not oxyR. In 72 h biofilms, katG and katE were the major protective genes. katG, ahpC and katE peroxide protection had both rpoS-dependent and rpoS-independent components, but katP protection was independent of rpoS. H(2)O(2) challenge induced (P<0.05) katG, ahpC and katP expression in biofilm cells, suggesting that peroxide induction of the OxyR-dependent resistance genes may contribute to the RpoS-independent protection in Shiga toxin-producing E. coli biofilms.
在许多大肠杆菌 O157:H7 血清型中，针对过氧化物损伤的防御机制包括过氧化物还原酶 AhpCF 和三种过氧化氢酶：KatG（过氧化氢酶/过氧化物酶）、KatE（过氧化氢酶）和质粒编码的 KatP（过氧化氢酶/过氧化物酶）。AhpC 和 KatG 的基础表达受 RpoS 维持，AhpC、KatG 和 KatP 都在指数生长期被 OxyR/σ(70)诱导。KatE 在静止生长期间受 RpoS 调控，并且不依赖于 OxyR。在之前的研究中，我们使用 ATCC 43895（EDL933）的突变株，在所有可能的组合中缺失 katG、ahpC、katE 和 katP，以研究在 37°C 的 LB 肉汤中指数生长和 18-24 小时生长期间的过氧化物抗性。在这项研究中，我们使用了三缺失株，这些株系分别分离出每个过氧化氢酶/过氧化物酶基因，以研究它们在 48 和 72 小时生物膜中 43895OR 形成变体的过氧化物抗性中的作用。我们还使用定量实时逆转录 PCR 和翻译 lacZ 融合来研究基因表达。过氧化物抗性在生物膜细胞中比在浮游细胞中更高（P<0.05），完全抗性需要 rpoS 但不需要 oxyR。在 72 小时生物膜中，katG 和 katE 是主要的保护基因。katG、ahpC 和 katE 的过氧化物保护既有 rpoS 依赖性的，也有 rpoS 非依赖性的，但 katP 的保护与 rpoS 无关。H 2 O 2 挑战诱导（P<0.05）生物膜细胞中 katG、ahpC 和 katP 的表达，表明 Shiga 毒素产生型大肠杆菌生物膜中 OxyR 依赖性抗性基因的过氧化物诱导可能有助于 rpoS 非依赖性保护。
