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Applied and Environmental Microbiology, October 2006, p. 6680-6686, Vol. 72, No. 10
0099-2240/06/$08.00+0     doi:10.1128/AEM.02952-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Virulence Factor Gene Profiles of Escherichia coli Isolates from Clinically Healthy Pigs

Peter Schierack,1* Hartmut Steinrück,2 Sylvia Kleta,1 and Wilfried Vahjen3

Institut für Mikrobiologie und Tierseuchen, Fachbereich Veterinärmedizin, Freie Universität Berlin, Berlin, Germany,1 Nationales Referenzlabor für E. coli, Bundesinstitut für Risikobewertung (BfR), Berlin, Germany,2 Institut für Tierernährung, Fachbereich für Veterinärmedizin, Freie Universität Berlin, Berlin, Germany3

Received 14 December 2005/ Accepted 17 June 2006

Nonpathogenic, intestinal Escherichia coli (commensal E. coli) supports the physiological intestinal balance of the host, whereas pathogenic E. coli with typical virulence factor gene profiles can cause severe outbreaks of diarrhea. In many reports, E. coli isolates from diarrheic animals were classified as putative pathogens. Here we describe a broad variety of virulence gene-positive E. coli isolates from swine with no clinical signs of intestinal disease. The isolation of E. coli from 34 pigs from the same population and the testing of 331 isolates for genes encoding heat-stable enterotoxins I and II, heat-labile enterotoxin I, Shiga toxin 2e, and F4, F5, F6, F18, and F41 fimbriae revealed that 68.6% of the isolates were positive for at least one virulence gene, with a total of 24 different virulence factor gene profiles, implying high rates of horizontal gene transfer in this E. coli population. Additionally, we traced the occurrence of hemolytic E. coli over a period of 1 year in this same pig population. Hemolytic isolates were differentiated into seven clones; only three were found to harbor virulence genes. Hemolytic E. coli isolates without virulence genes or with only the fedA gene were found to be nontypeable by slide agglutination tests with OK antisera intended for screening live cultures against common pathogenic E. coli serogroups. The results appear to indicate that virulence gene-carrying E. coli strains are a normal part of intestinal bacterial populations and that high numbers of E. coli cells harboring virulence genes and/or with hemolytic activity do not necessarily correlate with disease.

* Corresponding author. Mailing address: Institut für Mikrobiologie und Tierseuchen, Postfach 040225, D-10116 Berlin, Germany. Phone: 49-30-2093 6704. Fax: 49-30-2093 6067. E-mail: schierack.peter{at}vetmed.fu-berlin.de.

Applied and Environmental Microbiology, October 2006, p. 6680-6686, Vol. 72, No. 10
0099-2240/06/$08.00+0     doi:10.1128/AEM.02952-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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