Use of Fimbrial Rod for F18ab Fimbriae⁺ STEC Colonization to Host Cells

Type 1 fimbriae are important virulence determinants of some Gram-negative pathogens, which promote bacterial colonization. The fimbrial rod is primarily composed of multiple copies of the major fimbrial subunit FimA. FimH adhesin, however, is present as a fibrillar tip structure that drive bacteria binding to host cellular mannose containing receptor. Here, we provide protocols to evaluate and compare the function of type 1 fimbrial subunits in F18ab fimbriae⁺ Shiga toxin-producing Escherichia coli (STEC). We found that both FimA and FimH are required for bacterial adhesion, invasion, and biofilm formation. Deleting fimA gene showed much more reduction in bacterial adhesion and invasion to porcine intestinal columnar epithelial cells IPEC-J2, than that of fimH mutant. Biofilm formation was significantly reduced in both mutants with an equal level. In addition, qPCR demonstrated that either fimA or fimH deletion down-regulated the bacterial flagella and F18 fimbriae genes expression, while up-regulated adhesin was involved in diffuse adherence-I (AIDA-I) gene expression, suggesting the co-regulation of cell surface-localized adhesins in F18ab fimbriae⁺ STEC.