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P1-24 Virulence Factors Detected by Whole Genome Sequence Analysis of Shiga Toxin-producing Escherichia coli Isolated from Irrigation Water

Monday, August 1, 2016
America's Center - St. Louis
Pascal Delaquis, Agriculture and Agri-Food Canada, Summerland, Canada
Stephanie Nadya, University of British Columbia, Vancouver, Canada
Jessica Chen, University of British Columbia, Vancouver, Canada
Kevin Allen, University of British Columbia, Vancouver, Canada
Chad Laing, Public Health Agency of Canada, Lethbridge, Canada
Vic Gannon, Public Health Agency of Canada, Lethbridge, Canada
Susan Bach, Agriculture and Agri-Food Canada, Summerland, Canada
Ed Topp, Agriculture and Agri-Food Canada, London, Canada
Introduction: The characterization of microbiological hazards in irrigation water currently relies on prevalence data and broad assumptions about risks to human health. Information about the virulence of specific hazards can be derived from whole genome sequence (WGS) analysis.

Purpose: To compare virulence factors in Shiga toxin-producing Escherichia coli (STEC) isolated from irrigation waters in a defined geographic region of Canada with those found in human isolates.  

Methods: Annotated genomes of STEC isolated from irrigation water in the Fraser Valley of British Columbia, Canada, were searched with VirulenceFinder v. 1.4 to detect Shiga toxin (stx 1 and stx 2) and intimin gene (eaeA) allelic variants. Presence/absence of additional virulence factors were determined using the predictive genomics platform SuperPhy; statistical comparisons between water and human isolates were conducted using Fisher's exact test, and adjusted for multiple hypothesis testing using the false-discovery rate of Benjamini and Hochberg.

Results: A total of 47 STEC from 20 serotypes were recovered from water, including isolates from serogroups O157, O111, O26 and O103 bearing alleles for several Stx subtypes (stx1a, stx1c, stx2a, stx2b, stx2c or stx2d) and allelic variants of the eaeA gene (β1, θ, ε, γ and ζ). Comparison with 312 human isolates with similar serotypes indicated that 17 of 380 known virulence factors were statistically over-represented among the water isolates, while 40 were statistically over-represented in the human isolates.

Significance: The STEC isolates included serotypes containing complements of virulence factors present in strains with known association to human disease. Hence, WGS analysis confirmed that STEC in irrigation waters in the region represent a potential threat to human health.

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