Western
Meeting of Poultry
Clinicians and Pathologists
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Clinicians and Pathologists
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Escherichia coli Cellulitis in Broiler Chickens: Analysis of virulence factors Brenda Allan Veterinary Infectious Disease Organization
Cellulitis is characterized by an inflammation of the tissue under the skin. E. coli is the bacteria most frequently isolated from the lesions, although other bacteria have been found alone or in combination with E. coli. E. coli is a ubiquitous bacterium in the environment and in the intestinal tract of poultry. It is not clear if any E. coli can cause the disease or if only a subset of E. coli with specific properties are responsible for the infection. In addition, it is not known if a single isolate of E. coli causes all cellulitis observed in a flock or if several different types of E. coli may be involved in causing disease. In an effort to answer these questions we have examined 39 E. coli isolated from cellulitis lesions of chickens originating ten flocks. The isolates were characterized with respect to their O serogroup, multilocus enzyme electrophoresis (MLE) profile, and virulence factors. Analysis of the O serogroup was not very helpful in differentiating the isolates as 64 percent were non typeable. Of the isolates that were typeable only serogroup O25 and O78 were represented by more than one isolate. MLE analysis revealed four main genetic clusters of E. coli. These four groups encompassed 75% of the isolates. E. coli implicated in other avian diseases such as colisepticemia and swollen head syndrome have also been assigned to these clusters. The presence of virulence factors was assayed using biologic assays and genetic probes. In most cases good agreement was observed between the two techniques. Most isolates of E. coli produced pili and in some cases contained genes for more than one type of pili. All strains tested were resistant to killing by normal serum at a concentration of 60%. All isolates contained the genes for the production of aerobactin, an iron-sequestering siderophore, and in 85% of the isolates aerobactin could be detected by a biologic assay. Haemolysin production was not detected in any of the isolates. The virulence factors observed here are similar to those described in E. coli responsible for causing colisepticemia. It appears that the E. coli isolated from cases of cellulitis is similar to those that cause other diseases of poultry. In some cases all isolates from a single flock were identical, but in other cases an individual folk would have several distinct types of E. coli causing disease. |
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