Escherichia coli extraintestinal infections (ExPEC) cause significant disease in humans and companion animals (cats and dogs). These are mainly urinary tract infections, but can be more serious and include sepsis and neonatal meningitis. E coli inhabits the hindgut causing no problems until it gains access to the urinary tract. The common, close relationship of cats and dogs and the isolation of ExPEC strains from these pets las led to concern that they may serve as a possible reservoir. In this seminar I share some of my research findings to confirm that the most important human ExPEC strains can be isolated from faeces collected from domestic cats and dogs in Canberra. Importantly I found that one group , ST73, was very commonly isolated from cat faecal samples, at a higher prevalence than in samples from people in Canberra. By comparing phenotypic and genotypic attributes of cat and human isolates I found that host sharing of strains had occurred supporting zoonosis concerns. I also discovered that ST73 strains from each source are similar but have key differences. These differences could be related to host lifestyle and I found evidence that the unique cat diet can shape representation of E coli strains in the cat gut.