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ARS Home » Midwest Area » Ames, Iowa » National Animal Disease Center » Food Safety and Enteric Pathogens Research » Research » Publications at this Location » Publication #422840
Research Project: Intestinal Microbial Ecology and Non-Antibiotic Strategies to Limit Shiga Toxin-Producing Escherichia coli (STEC) and Antimicrobial Resistance Transmission in Food Animals

Location: Food Safety and Enteric Pathogens Research

Title: Variable curli-expression and non-curli factors influence Shiga toxin-producing Escherichia coli biofilm formation and animal cell adherence, respectively

Author
item BIERNBAUM, ERIKA - Oak Ridge Institute For Science And Education (ORISE)
item BARI, NAYEEMUL - Oak Ridge Institute For Science And Education (ORISE)
item DRABEK, KOY - Oak Ridge Institute For Science And Education (ORISE)
item Bayles, Darrell
item Kudva, Indira

Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 3/19/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Asymptomatic cattle and biofilms act as reservoirs for the foodborne pathogen, Shiga toxin-producing Escherichia coli (STEC), in animal production environments. Bacterial factors involved in STEC adherence to the bovine recto-anal junction squamous epithelial (RSE) cells, are still being characterized, while curli fimbriae are established components of biofilm formation. Recently, we explored the role of curli in STEC adherence to RSE cells, considering the aggregative adherence patterns demonstrated by some STEC on these cells. STEC O157, O26 and O111 strains, from different sources, with diverse DNA-fingerprints, and biofilm, virulence and toxin phenotypes, were evaluated. The STEC strains were either curli-positive (C+) or curli-negative (C-) with some strains comprising C+/C- curli-variants. Biofilms were produced at 26°C by all C+ isolates. The csgA gene, although present in all strains, was down-regulated in C- strains as determined by microscopy and RT-qPCR. The O157 and O111 strains demonstrated an aggregative-strong adherence pattern, while O26 strains were primarily diffuse-moderate/strong on RSE cells, irrespective of the curli/biofilm phenotype. This suggested that factors other than curli were enabling STEC adherence to RSE cells. To gain insights into csgA down-regulation and additional adherence factors, we evaluated, (1) other genes involved in curli biogenesis, (2) biofilm formation under different conditions, and (3) STEC transcriptomes under adherence assay conditions. Control strains and statistics were incorporated as needed. Sequence analysis of the curli-regulatory genes, rpoS, rcsB and mlrA, did not reveal any mutations except for one C-, O111 isolate that had an internal deletion in rpoS resulting in a premature stop codon. The csgA sequence was also conserved between isolates. Biofilm formation was tested in two media, LB-no salt (LB-NS) and DMEM-low glucose (DMEM-LG) used for biofilms and adherence assays respectively, at 26oC and/or at 37oC, with incubation for 2- or 5-days. Variable curli and biofilm phenotypes were observed, and some C- isolates produced weak biofilms post- 5-day incubation. Growth curve analysis using DMEM-LG verified fitness of all isolates selected for transcriptome analysis. We are presently analyzing other curli-structural genes (csgB–csgF), cellulose-production and the corresponding genes (bcsA-B), along with the transcriptome data to identify additional biofilm- and adherence- related factors that will be verified via knock-out mutagenesis.