Produce Safety and Microbiology Research Unit, Western Regional Research Center, Agricultural Research Service, US Department of Agriculture, Albany, CA, USA.
FEMS Microbiol Ecol. 2020 Mar 1;96(3). doi: 10.1093/femsec/fiaa014.
Pathogenic E. coli remains undigested upon phagocytosis by Tetrahymena and is egested from the ciliate as viable cells in its fecal pellets. Factors that are involved in the survival of Shiga toxin-producing E. coli serovar O157: H7 (EcO157) from digestion by Tetrahymena were identified by microarray analysis of its transcriptome in the protozoan phagosome. Numerous genes belonging to anaerobic metabolism and various stress responses were upregulated significantly ≥ 2-fold in EcO157 cells in the food vacuoles compared with in planktonic cells that remained uningested by the protist. Among these were the oxidative stress response genes, ahpF and katG. Fluorescence microscopy and staining with CellROX® Orange confirmed the presence of reactive oxygen species in food vacuoles containing EcO157 cells. Frequency distribution analysis of the percentage of EcO157 viable cells in Tetrahymena fecal pellets revealed that the ΔahpCF and ΔahpCFΔkatG mutants were less fit than the wild type strain and ΔkatG mutant after passage through the protist. Given the broad use of oxidants as sanitizers in the food industry, our observation of the oxidative stress response in EcO157 during its interaction with Tetrahymena emphasizes the importance of furthering our knowledge of the physiology of this human pathogen in environments relevant to its ecology and to food safety.
当志贺毒素产生大肠杆菌血清型 O157:H7（EcO157）被四膜虫吞噬时，它仍然未被消化，并作为活细胞从纤毛虫的粪便颗粒中排出。通过对其在原生动物吞噬体中的转录组进行微阵列分析，确定了逃避四膜虫消化的 EcO157 生存相关的因素。与未被原生动物吞噬的浮游细胞相比，在食物泡中的 EcO157 细胞中，许多属于厌氧代谢和各种应激反应的基因显著上调≥2 倍。其中包括氧化应激反应基因 ahpF 和 katG。荧光显微镜和 CellROX® Orange 染色证实，在含有 EcO157 细胞的食物泡中存在活性氧。通过四膜虫粪便颗粒中 EcO157 活细胞的百分比频率分布分析发现，与野生型菌株和 ΔkatG 突变体相比，ΔahpCF 和 ΔahpCFΔkatG 突变体在通过原生动物后适应性较差。鉴于氧化剂在食品工业中作为消毒剂的广泛应用，我们观察到 EcO157 在与四膜虫相互作用过程中的氧化应激反应，强调了进一步了解该人类病原体在与其生态学和食品安全相关的环境中的生理学的重要性。
