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P2-88 International Divergence of Bovine and Human Shiga Toxin-producing Escherichia coli O157:H7 Genotypes

Tuesday, August 5, 2014
Exhibit Hall D (Indiana Convention Center)
Patricia Jaros, Massey University, Palmerston North, New Zealand
Adrian Cookson, AgResearch Ltd, Palmerston North, New Zealand
Donald Campbell, Ministry for Primary Industries, Wellington, New Zealand
Gail Duncan, Ministry for Primary Industries, Wellington, New Zealand
Deborah Prattley, Massey University, Palmerston North, New Zealand
Thomas Besser, Washington State University, Pullman, WA
Smriti Shringi, Washington State University, Pullman, WA
Philip Carter, Institute of Environmental Science & Research Ltd, Porirua, New Zealand
Jonathan Marshall, Massey University, Palmerston North, New Zealand
Steve Hathaway, Ministry for Primary Industries, Wellington, New Zealand
Nigel French, Massey University, Palmerston North, New Zealand
Introduction: Shiga toxin-producing Escherichia coli (STEC) O157:H7 is a zoonotic pathogen of significant public health concern in many countries. Ruminants are asymptomatic carriers of STEC, shedding the pathogen via faeces, and are recognised as an important source of infection in humans.

Purpose: To compare the genotype distribution of bovine and human E. coli O157:H7 isolates from New Zealand (NZ), Australia (AU), and the United States (US) using Shiga toxin-encoding bacteriophage insertion (SBI) genotyping data, and assess evidence of E. coli O157:H7 transmission from cattle to humans for each country.

Methods: SBI typing is a multiplex PCR method for screening specific Shiga toxin (stx)-associated bacteriophage insertion sites and stx genes (stx1, and genetic subtypes stx2a and stx2c of stx2). The characters A, W, Y, S and 1, 2a, 2c represent bacteriophage insertion sites argW, wrbA, yehV, sbcB, and stx genes stx1, stx2a, stx2c, respectively. SBI types of 40, 205, and 143 bovine, and 363, 79, and 179 human E. coli O157:H7 isolates from NZ, AU, and the US, respectively, were evaluated. Proportional similarity indices (PSI) were computed based on the frequency distributions of SBI types to illustrate the epidemiological linkage between bovine and human isolates for each country.

Results: A distinct prevalence distribution of SBI types was observed between the countries. AY2a was predominant among NZ bovine and human isolates (55.0% and 57.9%, respectively), ASY12c was predominant among AU bovine and human isolates (51.7% and 43.0%, respectively), and WY12a was predominant among US bovine and human isolates (43.4% and 63.7%, respectively). NZ bovine and human genotypes shared the highest similarity (PSI value of 0.92) followed by AU (0.69) and the US (0.61).

Significance: Highly evident divergence of genotypes was demonstrated between NZ, AU, and the US but the reason for this is unknown. Possibilities include genetic drift and/or selection driven by different environmental factors, such as climate, types of feed, husbandry systems, or animal genetics. There was strong evidence for a close association between cattle and human populations of E. coli O157:H7 isolates in NZ, consistent with transmission of STEC from cattle to humans (or transmission to both hosts from another environmental reservoir).

Back to: Poster Session - Pathogens, Epidemiology, Novel Laboratory Methods, Food Defense, Communication Outreach and Education, General Microbiology, Dairy and Other Food Commodities, Food Toxicology
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