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Statement of Research Problem:
Enterohemorrhagic Escherichia coli (EHEC) of serotype O157:H7 are phenotypically distinct from typical
E. coli, in that they do not ferment sorbitol and do not exhibit glucuronidase (GUD) activity. They are also easily
identified by their ability to production Shiga toxins (Stx) and by the presence of the somatic O157 and the
flagellar H7 antigens. As a result, these traits are extensively utilized in methods used to isolate and detect O157:H7
in foods. However, new variant strains of EHEC, particularly O157:H7, are being isolated more frequently from foods,
animals and humans worldwide. These include sorbitol-fermenting variants, strains that exhibit GUD, non-motile, toxigenic
variants; serological variants; toxin non-producing strains, etc. These variants carry most of the trait EHEC virulence
markers, so are potentially pathogenic and some have already been implicated in illness; however, due to changes in trait
genotypic and phenotypic markers, EHEC variants elude detection by current testing methods.
Statement of Project Objective(s):
Genetically characterize pathogenic EHEC variants for trait markers and virulence genes and determine the factors causing
the expression or non-expression of trait markers in these EHEC strains. These studies will provide information to
account for the emergence of these variant strains by correlating the position of these variants in the existing
evolutionary model for O157:H7 (Feng, et al, JID, 1998) and also identify new genetic or phenotypic markers that can be
used to test for these emerging pathogenic variants. This work relates directly to the objectives of developing improved
technology for detecting emerging food-borne pathogens.
Anticipated Impact on FDA Regulatory Program:
Project Priority Changes During FY2000: None
Research Personnel:
Name | Office/Division | FTE [00, 01, 02] | Component |
---|---|---|---|
Peter Feng | OPDFB/DMS | 1.0, 1.0, 1.0 | 1 |
Steve Monday | OPDFB/DMS | 1.0, 1.0, 1.0 | 1 |
Total FTE: |
2.0, 2.0, 2.0 |
Component 1 Objectives:
To characterize the following phenotypic variants of O157:H7 and other EHEC serotypes and identify new markers for
developing detection assays.
Hypertext updated by dav 2001-OCT-02