Submitted to: Research Workers in Animal Diseases Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2007
Publication Date: 12/2/2007
Citation: Lippolis, J.D., Reinhardt, T.A. 2007. Adaptive changes in protein expression in Escherichia coli as a consequence of growth in milk [abstract]. Conference of Research Workers in Animal Diseases. p. 123.
Technical Abstract: Bacteria must adapt to the environment in the mammary gland and the pressures exerted by the host immune system in order to survive. Understanding bacterial adaptation to their environment could become a foundation to research into better therapeutics for treatment of bacterial infections. As a first step, shotgun proteomics was used to quantify protein changes in Escherichia coli (mastitis isolate) grown in either Luria-Bertoni broth or fresh unprocessed milk. Changes in expression for approximately 30% of the nearly 1000 proteins identified were obtained. Eight proteins involved in iron transport were identified with abundance data comparing growth in milk and bacterial growth media. Seven of the eight were up-regulated in bacteria grown in milk ranging from 3 to 9 fold. An innate mechanism to limit bacterial growth is the sequestration of free iron by proteins such a lactoferrin. Therefore, bacteria must increase expression of proteins that bind and internalize iron and our proteomic profiling suggests E. coli responded to the milk environment by increasing its own iron-binding proteins. Other proteins that may play a role in bacterial pathogenesis were identified. For example, Flagellin was down-regulated over 3 fold when bacteria were grown in milk. Flagellin is a ligand for the toll-like receptor 5 (TLR-5) molecule. TLR-5 is a member of a class of cell surface pattern recognition receptors that bind to various molecules from pathogens. TLR-5 receptor activation leads to activation of intracellular signaling pathways that lead to stimulation of the immune system. Therefore, down-regulation of Flagellin may be an immune surveillance escape mechanism employed by the bacteria to avoid detection by TLR-5. Critical to an infection is the ability of the bacteria to grow in the host. Despite the various antimicrobial agents in milk, bacteria have evolved to be able to overcome these defense mechanisms and grow in the mammary gland. These data demonstrate that quantitative shotgun proteomics has great potential to provide new insights into how bacteria adaptive to growth in milk and may provide new insights into therapies.