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.