Uropathogenic Escherichia coli (UPEC) and avian pathogenic Escherichia coli (APEC) are pathotypes of E. coli that can cause disease outside the intestinal tract, leading to major health and welfare issues for their respective hosts. Recent genomic studies have identified genetic similarities between these pathotypes, raising concerns about potential cross-species transmission.

The primary aim of this study was to investigate whether human UPEC, canine UPEC and APEC represent overlapping populations, with shared pathogenic potential. The pathotypes were characterised using both phenotypic and genotypic methods. Comparative genomic analysis found that UPEC genomes from human (n=48) and canine (n=154) hosts were more similar to each other than to APEC (n=56). However, distinct overlapping phylogenetic clusters containing genomes from all three host sources were identified.

To assess the pathogenic potential of the genetically similar isolates (human UPEC (n=3), canine UPEC (n=3), and APEC (n=3), in vitro adherence, invasion and cytotoxicity assays were performed using human intestinal (HT29), human bladder (5637), and avian intestinal (8E11) cell lines. No significant differences (p>0.05) were observed in bacterial-host cell interactions. However, the 8E11 cell line exhibited distinct cellular responses, including greater resilience to bacteria-induced cytotoxicity. These observations prompted further characterisation and investigation of host-pathogen interactions using light and electron microscopy.

Additionally, the respiration profiles of these human and canine UPEC and APEC were compared using Biolog phenotypic microarrays across 380 different chemical substrates or osmotic/ionic conditions. Of these, L-tryptophan was the only substrate where a significant difference in metabolic activity was observed, with UPEC exhibiting higher respiration compared to the APEC (p<0.05).

Overall, these findings demonstrate that a subset of UPEC and APEC isolates exhibited overlapping characteristics, suggesting the potential of population overlap and a risk of cross-host transmission. This highlights the importance of a One Health approach in estimating the risks posed by ExPEC.