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United States Department of Agriculture

Agricultural Research Service


item Besser, Thomas
item Shaikh, Nurmohammad
item Holt, Nicholas
item Tarr, Phillip
item Konkel, Michael
item Malik-kale, Preeti
item Walsh, Coilin
item Whittam, Thomas
item Bono, James - Jim

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2006
Publication Date: 2/1/2007
Citation: Besser, T.E., Shaikh, N., Holt, N.J., Tarr, P.I., Konkel, M.E., Malik-Kale, P., Walsh, C.W., Whittam, T.S., Bono, J.L. 2007. Greater diversity of shiga toxin-encoding bacteriophage insertion sites among Eschericha coli O157:H7 isolates from cattle than from humans. Applied and Environmental Microbiology. 73(3):671-679.

Interpretive Summary: Escherichia coli O157:H7 contains viruses which produce Shigatoxins, which are necessary to cause human disease. Previous work identified three groups of E. coli O157:H7 isolated from human patients that differed on the locations where the Shigatoxin-containing viruses were inserted into the bacterial chromosome. This current work describes a broader study of the virus insertion sites in cattle isolates and in additional human isolates. The major groups previously identified in human isolates were found to be the predominant ones among the new clinical isolates and were also identified among cattle isolates. However, 12 additional groups were identified, most of which were found only among cattle isolates. This study demonstrated that E. coli O157:H7 isolated from cattle are more diverse than those isolated from human patients, and raises the question of whether all the diverse groups of E. coli O157:H7 isolated from cattle are capable of causing disease in humans.

Technical Abstract: Background: Escherichia coli O157:H7, a zoonotic human pathogen with reservoir in domestic cattle, produces Shiga toxin(s) encoded by bacteriophages. Chromosomal insertion sites of these bacteriophages define three principal genotypes (Clusters 1 - 3 ) among clinical isolates of E. coli O157:H7. Methods: Stx-encoding bacteriophage insertion site genotypes were evaluated in 281 clinical and 80 bovine isolates. Results: 274 (97.9%) of the clinical, but only 41 (51.3%) of the bovine isolates belonged to Clusters 1, 2, or 3. Twelve additional genotypes were identified in human (one genotype), cattle and humans (one genotype), or cattle only (ten genotypes, accounting for 47.5% of the bovine isolates). Two other markers previously associated with isolates from cattle or with clinical isolates here showed tendencies by genotype groups within isolates from cattle; the tir allele sp-1 and Q933W allele were under- and over-represented, respectively, among Cluster 1 – 3 genotypes. Conclusions: Stx-encoding bacteriophage insertion site genotypes indicate the broader diversity of E. coli O157:H7 in the bovine reservoir compared to clinical isolates, consistent with the possibility of reduced virulence to humans of some animal E. coli O157:H7 genotypes.

Last Modified: 06/27/2017
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