|Besser, Thomas - WASHINGTON STATE UNIV.|
|Shaikh, Nurmohammad - WASHINGTON UNIV.|
|Tarr, Phillip - WASHINGTON UNIV.|
Submitted to: American Society of Microbiologists Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 17, 2006
Publication Date: May 1, 2006
Citation: Besser, T.E., Bono, J.L., Shaikh, N., Tarr, P.I. 2006. Shiga toxin bacteriophage insertion sites identify diverse Escherihica coli O157:H7 strain types with distributions biased to the bovine host reservoir [abstract]. American Society of Microbiologists. Poster No. Z-017. Technical Abstract: Background: The incidence of human disease caused by E. coli O157:H7 is surprisingly low considering its ubiquitous distribution (and frequently, high prevalence) in the bovine reservoir and its low infectious dose for humans. The purpose of this study was to detect E. coli O157:H7 strain types in the bovine host reservoir under-represented in human clinical isolates. Methods: Eighty bovine isolates of EHEC O157 selected to represent diverse cattle farms in each of four time periods from 1990 to 2004 were tested by PCR for genes representing the cardinal virulence factors of E. coli O157:H7: stx1 and stx2 , eaeA and tir. Strain types were identified by PCR detection of Shiga toxin encoding bacteriophage insertion sites (STX-IS). STX-IS types were then evaluated for two additional markers with biased distribution among bovine and human isolates; a tir sequence polymorphism (sp-1, Bono J et al., Abstract C-388. Discrimination of Escherichia coli O157:H7 Isolates by Genotyping Single Nucleotide Polymorphisms, ASM General Meeting, June 5-9, 2005, Atlanta GA) and the Q anti-terminator gene 933W allele. Results: All isolates contained eaeA and tir; all but one contained stx1 and/or stx2. Bovine isolates included 13 different STX-IS, two STX-IS (41 isolates) that matched the most frequently previously identified human clinical isolate types (H types) and eleven STX-IS (38 isolates) apparently novel to the bovine reservoir (B types). The tir polymorphism sp-1 occurred more frequently among B type than H type STX-IS (10/38 vs. 1/41, p=0.006). The 933W Q-anti-terminator allele occurred more frequently among H type than B type STX-IS (40/41vs. 22/38, p<0.001). Conclusion: STX-IS typing demonstrates diverse E. coli O157:H7 sub-populations highly biased to the bovine reservoir and representing a higher proportion of bovine isolates than previously reported markers. Investigation of the differences underlying the biased distributions of STX-IS strain types promises an improved understanding of E. coli O157:H7 pathogenesis.