Abstract
Enterotoxigenic Escherichia coli (ETEC) produces two types of enterotoxins, LTs and STs, as well as several colonization factors (CFs), including CS21, CS3 fimbriae, and flagellar structures. This study investigated how these structures contribute to ETEC colonization and the immune response in HT-29 and HuTu-80 intestinal cells. ETEC strains with single, double, and triple mutations in the lngA, cstH, and fliC genes were generated and confirmed using PCR and Western blotting. The colonization of HT-29 and HuTu-80 intestinal cells by the ETEC E9034A strain, which was fully sequenced using a hybrid approach involving both Illumina and Oxford Nanopore technologies, was used to generate the mutant and recombinant proteins. The colonization and adherence of E9034A and its mutants were assessed through colony-forming unit (CFU) counts. Cytokine levels were assessed using flow cytometry and analyzed via FlowJo 7.6.1. Quantitative analysis revealed that the absence of the lngA, cstH, and fliC genes significantly (p < 0.01) reduced ETEC adherence to HT-29 and HutU-80 cells. In addition, only ETEC strains expressing the FliC protein induced IL-8 secretion. These findings suggest that LngA, CstH, and FliC in ETEC E9034A enhance adherence to intestinal cells and trigger the release of IL-8.