Dissertation
STX-ENCODING BACTERIOPHAGE CONTENT OF ESCHERICHIA COLI O157:H7 IS ASSOCIATED WITH VIRULENCE IN A PIGLET MODEL AND WITH FREQUENCY OF ISOLATION FROM HUMAN DISEASE
Doctor of Philosophy (PhD), Washington State University
01/2011
Handle:
https://hdl.handle.net/2376/3514
Abstract
Enterohemorrhagic E. coli O157:H7 (EHEC O157) is an important cause of food and waterborne illness in the developed countries. Cattle are a reservoir host and a major source of human exposure via contaminated food. Shiga toxins (Stx) are an important cardinal virulence factors. EHEC O157 strains can be differentiated into several genotypes based on stx content and Stx-encoding bacteriophage insertion sites. Bovine-biased genotypes (BBG) are over-represented among cattle isolates, while clinical genotypes (CG) are over-represented among human disease-associated isolates. Since both BBG and CG are carried by cattle as similar prevalence and both typically express one or more Stx, we hypothesized that the difference in representation in human disease is due to reduced virulence potential of BBG compared to CG resulting from different Stx-encoding bacteriophages and/or different Stx gene variant content. We compared the virulence potential of human and bovine isolates of CG and BBG in a newborn conventional pig model. CG-challenged piglets experienced more severe disease accompanied by earlier and higher mortality than BBG-challenged piglets. The CG strains used in this study carried stx2a and produced significantly higher amounts of Stx, whereas the BBG strains carried the stx2c gene variant only. Genomes of four BBG and three CG strains were compared using optical mapping technology to identify bacteriophage mediated differences. BBG strains were found to consistently differ from CG strains in the insertion sites of the Stx2 encoding phages in their chromosome, and specific bacteriophage / insertion site combinations correlated with the stx2 gene variant content of both BBG and CG strains. Multiplex-PCR based testing of 419 additional EHEC O157 strains confirmed these differences in the predominant stx2 variant content and their respective encoding bacteriophages in BBG strains and CG strains: BBG strains typically carry a Stx2c-encoding bacteriophage in sbcB and stx2c is typically their sole Stx2 gene, while CG strains typically carry a Stx2a-encoding bacteriophage in wrbA or argW and stx2a. These results suggest that BBG are less virulent than CG and their differential virulence may simply result from the presence of different stx2 variants, the encoding-bacteriophages and/or the amount of Stx produced.
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- Title
- STX-ENCODING BACTERIOPHAGE CONTENT OF ESCHERICHIA COLI O157:H7 IS ASSOCIATED WITH VIRULENCE IN A PIGLET MODEL AND WITH FREQUENCY OF ISOLATION FROM HUMAN DISEASE
- Creators
- Smriti Shringi
- Contributors
- Thomas E. Besser (Advisor)Dale D. Hancock (Committee Member)Carolyn H. Bohach (Committee Member)Douglas R. Call (Committee Member)Kelly A. Brayton (Committee Member)Kevin K. Lahmers (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Veterinary Medicine, College of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 87
- Identifiers
- 99900581750901842
- Language
- English
- Resource Type
- Dissertation