Epidemiology and Infection



Correlation between geographic distance and genetic similarity in an international collection of bovine faecal Escherichia coli O157[ratio]H7 isolates


M. A. DAVIS a1c1, D. D. HANCOCK a1, T. E. BESSER a2, D. H. RICE a1, C. J. HOVDE a3, R. DIGIACOMO a4, M. SAMADPOUR a5 and D. R. CALL a2
a1 Field Disease Investigation Unit, Department of Veterinary Clinical Sciences, Washington State University, Pullman, WA 99164, USA
a2 Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164, USA
a3 Department of Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, ID 83844, USA
a4 Division of Epidemiology, School of Public Health and Community Medicine, University of Washington, Seattle, WA 98195, USA
a5 Department of Environmental Health, School of Public Health and Community Medicine, University of Washington, Seattle, WA 98195, USA

Article author query
davis m   [PubMed][Google Scholar] 
hancock d   [PubMed][Google Scholar] 
besser t   [PubMed][Google Scholar] 
rice d   [PubMed][Google Scholar] 
hovde c   [PubMed][Google Scholar] 
digiacomo r   [PubMed][Google Scholar] 
samadpour m   [PubMed][Google Scholar] 
call d   [PubMed][Google Scholar] 

Abstract

Evidence from epidemiological and molecular studies of bovine Escherichia coli O157[ratio]H7 suggests that strains are frequently transmitted across wide geographic distances. To test this hypothesis, we compared the geographic and genetic distance of a set of international bovine Escherichia coli O157[ratio]H7 isolates using the Mantel correlation. For a measure of genetic relatedness, pulsed-field gel electrophoresis of six different restriction enzyme digests was used to generate an average Dice similarity coefficient for each isolate pair. Geographic distance was calculated using latitude and longitude data for isolate source locations. The Mantel correlation between genetic similarity and the logarithm of geographic distance in kilometers was −0·21 (P<0·001). The low magnitude of the Mantel correlation indicates that transmission over long distances is common. The occurrence of isolates from different continents on the same cluster of the dendrogram also supports the idea that Escherichia coli O157[ratio]H7 strains can be transferred with considerable frequency over global distances.

(Accepted March 28 2003)


Correspondence:
c1 Department of Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, ID 83844, USA.


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