Avian pathogenic Escherichia coli (APEC) is an economically important respiratory pathogen of chickens worldwide. Factors previously associated with the virulence of APEC include adhesins, iron-scavenging mechanisms, the production of colicin V (ColV), serum resistance, and temperature-sensitive hemagglutination, but virulence has generally been assessed by parenteral inoculation, which does not replicate the normal respiratory route of infection. A large plasmid, pVM01, is essential for virulence in APEC strain E3 in chickens after aerosol exposure. Here we establish the size of pVM01 to be approximately 160 kb and show that the putative virulence genes iss (increased serum survival) and tsh (temperature-sensitive hemagglutinin) and the aerobactin operon are on the plasmid. These genes were not clustered on pVM01 but, rather, were each located in quite distinct regions. Examination of APEC strains with defined levels of respiratory pathogenicity after aerosol exposure showed that both the aerobactin operon and iss were associated with high levels of virulence in APEC but that the possession of either gene was sufficient for intermediate levels of virulence. In constrast, the presence of tsh was not necessary for high levels of virulence. Thus, both the aerobactin operon and iss are associated with virulence in APEC after exposure by the natural route of infection. The similarities between APEC and extraintestinal E. coli infection in other species suggests that they may be useful models for definition of the role of these virulence genes and of other novel virulence genes that may be located on their virulence plasmids.

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The equine disease strangles, which is characterized by the formation of abscesses in the lymph nodes of the head and neck, is one of the most frequently diagnosed infectious diseases of horses around the world. The causal agent, Streptococcus equi subspecies equi , establishes a persistent infection in approximately 10 % of animals that recover from the acute disease. Such ‘carrier’ animals appear healthy and are rarely identified during routine veterinary examinations pre-purchase or transit, but can transmit S. equi to naïve animals initiating new episodes of disease. Here, we report the analysis and visualization of phylogenomic and epidemiological data for 670 isolates of S. equi recovered from 19 different countries using a new core-genome multilocus sequence typing (cgMLST) web bioresource. Genetic relationships among all 670 S. equi isolates were determined at high resolution, revealing national and international transmission events that drive this endemic disease in horse populations throughout the world. Our data argue for the recognition of the international importance of strangles by the Office International des Épizooties to highlight the health, welfare and economic cost of this disease. The Pathogenwatch cgMLST web bioresource described herein is available for tailored genomic analysis of populations of S. equi and its close relative S. equi subspecies zooepidemicus that are recovered from horses and other animals, including humans, throughout the world. This article contains data hosted by Microreact.

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.

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