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Applied and Environmental Microbiology, January 2007, p. 83-91, Vol. 73, No. 1
0099-2240/07/$08.00+0     doi:10.1128/AEM.00990-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Comparative Analysis of Virulence Genes, Genetic Diversity, and Phylogeny of Commensal and Enterotoxigenic Escherichia coli Isolates from Weaned Pigs{dagger} ,{triangledown}

Xi-Yang Wu,1,2 Toni Chapman,1,3 Darren J. Trott,3 Karl Bettelheim,4 Thuy N. Do,3 Steve Driesen,5 Mark J. Walker,2 and James Chin1,3*

Immunology and Molecular Diagnostic Research Unit, Elizabeth Macarthur Agriculture Institute, NSW DPI, Camden, New South Wales 2570, Australia,1 School of Biological Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia,2 School of Veterinary Science, The University of Queensland, Brisbane, Queensland 4072, Australia,3 Department of Microbiology and Immunology, University of Melbourne, Melbourne, Victoria 3010, Australia,4 Department of Primary Industry, P.O. Box 3100, Bendigo, Victoria 3554, Australia5

Received 26 April 2006/ Accepted 9 October 2006

If the acquisition of virulence genes (VGs) for pathogenicity were not solely acquired through horizontal gene transfers of pathogenicity islands, transposons, and phages, then clonal clusters of enterotoxigenic Escherichia coli (ETEC) would contain few or even none of the VGs found in strains responsible for extraintestinal infections. To evaluate this possibility, 47 postweaning diarrhea (PWD) ETEC strains from different geographical origins and 158 commensal E. coli isolates from the gastrointestinal tracts of eight group-housed healthy pigs were screened for 36 extraintestinal and 18 enteric VGs using multiplex PCR assays. Of 36 extraintestinal VGs, only 8 were detected (fimH, traT, fyuA, hlyA, kpsMtII, k5, iha, and ompT) in the ETEC collection. Among these, hlyA ({alpha}-hemolysin) and iha (nonhemagglutinating adhesin) occurred significantly more frequently among the ETEC isolates than in the commensal isolates. Clustering analysis based on the VG profiles separated commensal and ETEC isolates and even differentiated serogroup O141 from O149. On the other hand, pulsed-field gel electrophoresis (PFGE) successfully clustered ETEC isolates according to both serotype and geographical origin. In contrast, the commensal isolates were heterogeneous with respect to both serotype and DNA fingerprint. This study has validated the use of VG profiling to examine pathogenic relationships between porcine ETEC isolates. The clonal relationships of these isolates can be further clarified by PFGE fingerprinting. The presence of extraintestinal VGs in porcine ETEC confirmed the hypothesis that individual virulence gene acquisitions can occur concurrently against a background of horizontal gene transfers of pathogenicity islands. Over time, this could enable specific clonotypes to respond to host selection pressure and to evolve into new strains with increased virulence.

* Corresponding author. Mailing address: Elizabeth Macarthur Agricultural Institute, NSW DPI, PMB 8, Camden, NSW 2570, Australia. Phone: (61) 246406363. Fax: (61) 246406363. E-mail: james.chin{at}dpi.nsw.gov.au.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

{triangledown} Published ahead of print on 20 October 2006.

Applied and Environmental Microbiology, January 2007, p. 83-91, Vol. 73, No. 1
0099-2240/07/$08.00+0     doi:10.1128/AEM.00990-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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