Proteomics of Diverse Clonal Groups of Enterotoxigenic Escherichia coli Underline Variations in Surface Antigens and Similarities in Metabolism

Enterotoxigenic Escherichia coli (ETEC) is an important cause of diarrhoea, a pervasive disease in low- and middle-income countries that affects mostly young children and visiting travellers. Substantial diversity exists among ETEC isolates, hindering development of effective preventive means. To investigate how ETEC genomic variation is reflected at expressed proteome level, we applied label-free quantitative proteomics to 7 human ETEC strains representing 5 epidemiologically important lineages. We further determined the protein profile of the non-pathogenic E. coli B strain BL21 to discriminate metabolic features specific for ETEC. The analysis yielded a dataset of 2,894 proteins, of which 1,777 were present in all strains. Each ETEC strain displayed on average 27 (±10) proteins with known or putative links to virulence, both plasmid- and chromosomally-encoded, and a number of strain-specific isoforms participating in the biosynthesis of surface antigens. Statistical comparison of relative protein levels between the ETEC strains and BL21 revealed several proteins with significantly increased amounts only in BL21, including enzymes of arginine biosynthesis and metabolism of melibiose, galactitol and gluconate. ETEC strains displayed consistently increased levels of proteins that were functional in iron acquisition, maltose metabolism, and acid resistance. These results suggest that specific metabolic functions are shared among ETEC isolates.