Aims: In this study, we evaluated the phenotypic virulence characteristics of avian pathogenic Escherichia coli (APEC) isolates from broiler breeders with colibacillosis in Mississippi. Also, the relationship between phenotypic and genotypic virulence patterns was determined.
Methods and results: Twenty-eight APEC isolated from lesions of broiler breeders diagnosed with colibacillosis were used for embryo lethality assay and chick challenge study. The percentage of embryo mortality following embryo lethality assay and pathogenicity score following the chick challenge study were used to categorize the isolates based on virulence. Pearson correlation analysis was performed to determine the relationship between embryo mortality, chick pathogenicity, and the presence of virulence-associated genes in the isolates. Overall, 39.3% of the isolates were highly virulent and 3.5% were avirulent, following both assays. There existed a positive correlation between embryo mortality and chick pathogenicity (r = 0.73, P < .01), as well as percentage embryo mortality and pathogenicity score with the presence of some virulence genes.
Conclusions: Even though all the APEC were isolated from lesions of diseased breeders, the virulence potential varied from being avirulent to highly virulent. Further, we identified a positive relationship between phenotypic virulence and the frequency of virulence-associated genes.
Keywords: Avian pathogenic Escherichia coli; broiler breeder; chick virulence assay; embryo lethality assay; virulence characterization.
© The Author(s) 2024. Published by Oxford University Press on behalf of Applied Microbiology International.