4:10-4:30 p.m., Tuesday

, BVSc, PhD
Associate Director, Huck Institutes of the Life Sciences, & Professor of Microbiology and Infectious Diseases, Department of Veterinary and Biomedical Sciences,
Penn State University, University Park, PA 16802

Comparative genomic analysis and adherence mechanisms of super-shedder strains of Escherichia coli O157:H7

Robab Katani1*, Matthew R. Moreau1, Indira T. Kudva2, Maria T. Brandl 3, Michelle Q. Carter 3, Juan Antonio Raygoza Garay1, Rebecca Cote1, Lingling Li1, Terrance M. Arthur4, Chitrita DebRoy1, Michael M. Mwangi1, and Vivek Kapur 1. Corresponding author: Vivek Kapur, vkapur@psu.edu.

Shiga toxin-producing Escherichia coli O157:H7 (O157) cause foodborne infections and are of major public health concern. Asymptomatic cattle are the primary reservoir of O157 and harbor the pathogen at the terminal recto-anal junction (RAJ). A small subset of cattle, termed supershedders (SS), shed O157 at a rate that is several orders of magnitude greater than other colonized cattle, and epidemiological studies suggest that that SS cattle are responsible for 99% of the O157 shed into the environment.

To better understand the molecular mechanisms contributing to the supershedding, we recently reported the complete genome sequences of two SS strains of O157, SS17 (Accession No. CP008805), and SS52 (Accession No. CP010304). S17 has a ~5.5MB circular chromosome and two plasmids, pO157 and pSS17 that are 95kb and 37kb, respectively. The closed circular genome of SS52 is ~5.4Mbp with one plasmid, pO157 that is ~94kb. Whole genome alignments suggest that both SS strains cluster closely with the lineage I/II spinach outbreak isolates (EC4115 and TW14359) as compared with lineage I outbreak isolates (Sakai and EDL933) or the bovine lineage II isolates.

Our recent studies have showed marked differences between SS and non-SS strains in the adherence phenotype on bovine stratified squamous epithelial (RSE) cells wherein all tested (n=10) SS isolates showed a strong hyper-aggregative phenotype on RSE cells distinct from moderate, diffuse adherence observed on HEp-2 cells [PLoS One 10(2):e0116743, 2015]. To better understand the molecular mechanisms associated with this hyper-aggregative phenotype, we constructed a series of targeted deletions in candidate adherence loci in SS strains. Intriguingly, the results reveal that targeted deletions in the fim operon encoding type I pili showed altered adherence of some SS strains on both HEp-2 and RSE cells, providing strong evidence for a potential role of fimH in the adherence of bovine SS isolates to bovine RSE cells. These findings are particularly noteworthy since prior studies have showed that the fim operon is either not expressed or not active in O157:H7 isolates, but this may not be the case in SS strains. Taken together, the results suggest that these comparative genomics investigations are providing key insights on the molecular mechanisms of super-shedding in E. coli.

1. Department of Veterinary and Biomedical Science, Pennsylvania State University, University Park, Pennsylvania, USA; 2. Food Safety and Enteric Pathogen Research Unit, National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture (USDA), Ames, IA; 3. Produce Safety and Microbiology Research Unit, USDA-ARS, CA; 4. Roman L. Hruska U.S. Meat Animal Research Center, Agricultural Research Service, U.S. Department of Agriculture (USDA), Clay Center, Nebraska, USA.