Experimental induced avian E. coli salpingitis: Significant impact of strain and host factors on the clinical and pathological outcome

•The virulence of five isolates of Escherichia coli of various origins was assessed in an avian ascending model.•The pathological outcomes had major variations with-in and between groups. For all isolates the pathology scores were higher for broiler breeders compared to layers.•The severity of ascending E. coli infections in poultry seem to depend on both individual host factors and the strain characteristics, but not necessarily on the origin of the strain.

Several types of Escherichia coli have been associated with extra-intestinal infections in poultry, however, they may vary significantly in their virulence potential.The aim of the present study was to investigate the virulence of five strains of E. coli obtained from different disease manifestations or from the cloacae of a healthy chicken. The virulence potential of the strains were evaluated in an avian experimental model for ascending infections, and experiments were conducted in both layers and broiler breeders. The clinical outcome of infection was highly depending on the challenge strain, however, not significantly reflecting the origin of the strain. In general, broiler breeders had a more severe clinical outcomes of infection compared to layers, but major with-in group diversity was observed for all challenge strains of clinical origin. A single strain of ST95 (phylogroup B2) had a distinct ability to cause disease.Results of the study shows major differences in virulence of different strains of E. coli in ascending infections; however, there was no indication of tissue-specific adaptation, since strains obtained from lesions unrelated to the reproductive system were fully capable of causing experimental infection. In conclusion, the study provides evidence for the clinical outcome of infection with E. coli in poultry is largely influenced by the specific strain as well as individual host factors.