Proteomic Changes in Escherichia coli When Grown in Fresh Milk versus Laboratory Media

To establish an infection, bacteria must first adapt to the host environment and grow. For mastitis, the media in which bacteria must adapt to is milk. Mammary pathogenic Escherichia coli may express factors that are important for these bacteria to grow in milk and establish both acute and chronic infections of the mammary gland. We have used shotgun expression proteomics to determine the changes in protein expression when E. coli were grown in laboratory media compared to bacteria grown in whole fresh bovine milk. We report the expression data of approximately 1000 proteins. We found many proteins involved in the metabolism of lactose and various amino acids were up-regulated when bacteria were grown in milk. In addition, the LuxS protein was up-regulated when bacteria were grown in milk; this protein is associated bacterial quorum sensing as well as the expression of mobility proteins, such as flagellar components, and a number of genes associated with virulence. Growth of a mammary pathogenic E. coli in milk results in the up- and down-regulation of hundreds of proteins, some of which may be important to the pathogenesis of this organism.

细菌要建立感染，首先必须适应宿主环境并完成增殖。针对乳房炎而言，细菌需要适应的宿主环境介质为牛乳。乳腺致病性大肠杆菌（Mammary pathogenic Escherichia coli）可表达相关因子，这些因子对细菌在牛乳中增殖，并引发乳腺的急性与慢性感染至关重要。本研究采用鸟枪表达蛋白质组学（shotgun expression proteomics），对比分析了大肠杆菌（Escherichia coli，简称E. coli）在实验室培养基与全脂鲜牛乳中培养时的蛋白质表达变化，共获得约1000种蛋白质的表达数据。研究发现，当细菌在牛乳中培养时，诸多参与乳糖与各类氨基酸代谢的蛋白质表达量均会上调。此外，LuxS蛋白的表达量亦会上调；该蛋白与细菌群体感应（quorum sensing）、运动相关蛋白（如鞭毛组分）的表达，以及多种毒力相关基因的调控密切相关。乳腺致病性大肠杆菌在牛乳中培养时，会导致数百种蛋白质的表达量出现上调或下调，其中部分蛋白可能与该病原菌的致病机制密切相关。