Shiga toxin-producing Escherichia coli curli fimbriae have disparate roles in biofilm formation versus animal cell adherence

Authors: BEIRNEBAUM, ERIKA - Oak Ridge Institute For Science And Education (ORISE); MAZON, HANNAH - Former ARS Employee; DRABEK, KOY - Oak Ridge Institute For Science And Education (ORISE); Kudva, Indira

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 3/25/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Introduction: Asymptomatic cattle and biofilms contribute towards environmental dissemination of Shiga toxin-producing Escherichia coli (STEC). Purpose: Evaluate the role of STEC curli fimbriae, that contributes to biofilm formation, in adherence to bovine rectoanal-junction squamous epithelial (RSE) cells. Method: A total of thirty STEC O157, O26 and O111 strains, from different sources, with diverse biofilm and virulence phenotypes, were evaluated. Polymorphic amplified typing sequences (PATS) profiles and EHEC-ELISA based Shiga toxin (Stx) expression was determined. Curli expression was tested on congo-red indicator (CRI) plates, and biofilm formation in LB-No Salt media at 26°C for 2 and/or for 5 days. The presence and expression of the curli structural gene, csgA, was determined by PCR, immunofluorescence (IF) staining and RT-qPCR. STEC adherence to bovine RSE cells was evaluated by IF. One-way ANOVA and student t-tests were used as needed to evaluate statistical significance. Results: STEC grouped into 17 unique PATS profiles and strains without stx1 (5/30) expressed less Stx. Overall STEC strains were either curli-positive (C+) or curli-negative (C-) on the CRI plates but several strains comprised C+/C- variants. Biofilms were produced by all C+ strains/variants; differences were observed between 2 versus 5 days incubation. The csgA gene was amplified from all strains, however, the C- strains/variants lacked curli structures with statistically significant decrease in csgA expression. On bovine RSE cells, all O157 and O111 strains demonstrated an aggregative-strong adherence pattern, while O26 strains were primarily diffuse-moderate/strong irrespective of the curli/biofilm phenotype. This observation supports a role for mechansims other than curli in STEC adherence to the bovine RSE cells. Cellulose, another major biofilm component, may be evaluated for its compensatory role in subsequent experiments given that some C- strains/variants also produced transient biofilms. Significance: STEC curli contributes to biofilm formation but has no role in bovine RSE cell adherence. Presence of csgA does not always correlate with curli expression and curli variants can confound assays.