Understanding the pathogenic process of uropathogenic Escherichia coli ST127 using proteomics on uroepithelial co-culture samples

Uropathogenic Escherichia coli (UPEC) is the most common cause of urinary tract infection (UTI). Strains of sequence type (ST) 127 exhibit the highest virulence potential of most UPEC strains, but little is known about pathogenicity during infection. We sought to investigate this using a quantitative proteomics approach.

Three strains of UPEC ST127 (EC18, EC41 and SA189), in addition to non-pathogenic strain E. coli K12, were analysed in co-culture with the uroepithelial cell-line HT1197 for 5 h. We analyzed the bacterial and uroepithelial proteome along with the secreted proteins in the medium (secretome). The digested proteins and peptides from all fractions were separated on a Dionex Ultimate 3000 RSLC nano flow system and analyzed in an Orbitrap Velos Pro FTMS. Data were processed using Persues software.

Label free quantitative proteomics revealed different proteomic profiles of the co-cultured strains. Gene Ontology enrichmentanalysis showed upregulation in the pentose phosphate pathway and glycolysis/glycogenesis in EC18 (an O-antigen deficient mutant). These two pathways could be important routes of carbon flux through the central metabolic pathways during growth in urine. Co-culture of SA189 with HT1197 cells leads to apparent cytotoxic effects in HT1197 cells not seen with other UPEC strains. Analysis of the SA189 secretome revealed highly abundant bacterial proteins, some of which (e.g. aromatic-amino-acid aminotransferase) were uniquely found during co-culture conditions.

Proteomics is crucial towards increasing our understanding of the pathogenic potential of UPEC ST127 strains and may facilitate identification of novel diagnostic or therapeutic targets to reduce UTI.