proteomic analysis of enterotoxigenic escherichia coli etec in neutral and alkaline conditions background enterotoxigenic escherichia coli etec is a major cause of diarrhea in children and travelers to endemic areas secretion of the heat labile ab5 toxin lt is induced by alkaline conditions in this study we determined the surface proteome of etec exposed to alkaline conditions ph 9 as compared to neutral conditions ph 7 using a lpi hexalane flowcell combined with quantitative proteomics relative quantitation with isobaric labeling tmt was used to compare peptide abundance and their corresponding proteins in multiple samples at msms level for protein identification and quantification samples were analyzed using either a 1dlcms or a 2dlcms approachresults strong upregulation of the atp synthase operon encoding f1fo atp synthase and downregulation of proton pumping proteins nuof nuog ndh and wrba were detected among proteins involved in regulating the proton and electron transport under alkaline conditions reduced expression of proteins involved in osmotic stress was found at alkaline conditions while the secdependent transport over the inner membrane and outer membrane protein proteins such as ompa and the barrel assembly machinery bam complex were upregulatedconclusions etec exposed to alkaline environments express a specific proteome profile characterized by upregulation of membrane proteins and secretion of lt toxin alkaline microenvironments have been reported close to the intestinal epithelium and the alkaline proteome may hence represent a better view of etec during infection