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The conserved portion of the putative virulence region contributes to virulence of avian pathogenic Escherichia coli

Kelly A. Tivendale

Department of Veterinary Science, The University of Melbourne, Parkville, Victoria 3010, Australia

Correspondence
Glenn F. Browning
glenfb{at}unimelb.edu.au

Colibacillosis is a common systemic disease of worldwide economic importance in poultry, caused by Escherichia coli. E. coli are normally found in the intestines of poultry, but some strains are able to cause extraintestinal disease. Plasmid pVM01 is essential for virulence in avian pathogenic Escherichia coli (APEC) strain E3 in chickens after aerosol exposure and contains the virulence-associated genes iucA, iss and tsh in distinct regions. The determination of the complete sequence of this plasmid identified many ORFs that were highly similar to genes found in the APEC O1 plasmid, as well as many hypothetical ORFs. Truncated versions of pVM01 were constructed and introduced into avirulent APEC strain E3/2.4 and the pathogenicity of these strains was assessed by aerosol exposure. The function of the region of pVM01 that contains the genes for conjugation was confirmed. Strains carrying the truncated plasmids appeared to be of intermediate virulence compared to the wild-type APEC strain E3. The conserved portion of the putative virulence region was found to contribute to the colonization of and generation of lesions in the air sacs. Both the conserved and variable portions of the putative virulence region were shown to contribute to the colonization of the trachea, but the variable portion of the putative virulence region was not required for the strain to confer a virulent phenotype. These results reveal that deletion of the conserved portion of the putative virulence region, but not the variable portion of the putative virulence region, is associated with a decrease in virulence of APEC.

Present address: VMRI#2, Iowa State University, 1802 University Blvd, Ames, IA 50011, USA.

The GenBank accession number for the complete sequence of pVM01 reported in this paper is EU330199.

A supplementary table listing the predicted coding sequences of pVM01 is available with the online version of this paper.

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