Genomic Structure of an E. coli O157:H7 Super-Shedder Isolate with Increased Adherence to Bovine RSE Cells

Open Access
- Author:
- Cote, Rebecca Ann
- Graduate Program:
- Immunology and Infectious Diseases
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 21, 2013
- Committee Members:
- Vivek Kapur, Thesis Advisor/Co-Advisor
Subhashinie Kariyawasam, Thesis Advisor/Co-Advisor
Edward G Dudley, Thesis Advisor/Co-Advisor
Chitrita Debroy, Thesis Advisor/Co-Advisor - Keywords:
- E. coli
super-shedders
genome
sequencing
RSE cells - Abstract:
- Shiga toxin-producing Escherichia coli (STEC), in particular E. coli O157:H7, is recognized as a significant foodborne pathogen and a serious threat to public health worldwide. The major reservoir of E. coli O157:H7 are asymptomatic cattle which harbor the organism in the terminal recto-anal junction (RAJ) of their intestinal tract. Recently, isolates of E. coli O157:H7 have been obtained from cattle that are classified as “super-shedder”; excreting bacteria levels that are greater than 104 CFU/g of feces. In this study, we examined the genome of a super-shedder isolate (SS17) and conducted comparative analysis with reference strains of E. coli O157:H7. Analysis of the genome revealed a genome size of 5.5 Mb, 5442 coding DNA sequences (CDS), and a G+C content of 50.5%. In addition, SS17 has a Shiga toxin gene profile of stx1- stx2+ stx2c+ and contains two plasmids, pO157 and pSS17. Whole genome comparative analysis revealed a clustering of SS17 with the lineage I/II E. coli O157:H7 spinach outbreak strains, TW14359 and EC4115. In addition, analysis of phage regions in SS17 shows similar location and composition to the phage regions in TW14359 and EC4115. Of particular importance are virulence and adherence genes that may contribute to the super-shedder phenotype. A number of non-synonymous single nucleotide polymorphisms (nsSNPs) were identified in virulence and adherence genes including the adhesins wzzB, fimA, and csgG, along with a truncation of cah. Using a unique RAJ model, SS17 demonstrated an enhanced adherence pattern to bovine RSE cells as compared to other well-characterized E. coli O157:H7 strains. In addition, adherence of SS17 and reference O157 strains to RSE cells was not blocked in the presence of antisera to intimin, Tir, EspA, and EspB, suggesting a mechanism of adherence independent of these LEE-encoded proteins.