Greater Diversity of Shiga Toxin-Encoding Bacteriophage Insertion Sites among Escherichia coli O157:H7 Isolates from Cattle than in Those from Humans

Authors

Thomas E. Besser, Washington State UniversityFollow
Nurmohammad Shaikh, Washington State University
Nicholas J. Holt, Washington State University
Phillip I. Tarr, Washington State University
Michael E. Konkel, Washington State UniversityFollow
Preeti Malik-Kale, Washington State University
Coilin W. Walsh, Michigan State University
Thomas S. Whittam, Michigan State University
James L. Bono, Animal Health Research Unit, U.S. Meat Animal Research Center, ARS, USDA, Clay Center, NebraskaFollow

Date of this Version

February 2007

Comments

Published in APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Feb. 2007, p. 671–679.

Abstract

E. coli O157:H7, a zoonotic human pathogen for which domestic cattle are a reservoir host, produces a Shiga toxin(s) (Stx) encoded by bacteriophages. Chromosomal insertion sites of these bacteriophages define three principal genotypes (clusters 1 to 3) among clinical isolates of E. coliO157:H7. Stx-encoding bacteriophage insertion site genotypes of 282 clinical and 80 bovine isolates were evaluated. A total of 268 (95.0%) of the clinical isolates, but only 41 (51.3%) of the bovine isolates, belonged to cluster 1, 2, or 3 (P < 0.001). Thirteen additional genotypes were identified in isolates from both cattle and humans (four genotypes), from only cattle (seven genotypes), or from only humans (two genotypes). Two other markers previously associated with isolates from cattle or with clinical isolates showed similar associations with genotype groups within bovine isolates; the tir allele sp-1 and the Q_933W allele were under- and overrepresented, respectively, among cluster 1 to 3 genotypes. Stx-encoding bacteriophage insertion site typing demonstrated that there is broad genetic diversity of E. coli O157:H7 in the bovine reservoir and that numerous genotypes are significantly underrepresented among clinical isolates, consistent with the possibility that there is reduced virulence or transmissibility to humans of some bovine E. coli O157:H7 genotypes.