Invasion and intracellular proliferation of non-pathogenic E. coli in model infection systems

Uropathogens are typically distinguished from commensal or laboratory E. coli strains by defined pathogenic behaviours. In this study, we compared the behaviour of non-pathogenic Escherichia coli to that of uropathogenic E. coli in diverse infection models at a single-cell level using live-cell fluorescence microscopy. Using in vitro microfluidics and ex vivo mouse urinary tract infection model systems, we demonstrated that the standard laboratory E. coli strain MG1655 can behave like a pathogen, invading and proliferating inside human and mouse urothelial cells. Upon exposure to stress by the addition of urine, we observed that MG1655 undergoes infection-related filamentation, and then subsequent reversal back to rod shape when the stress is removed. This observation supports that infection-related filamentation should be regarded as a stress response rather than a virulence factor. Taken together, our results show that under infection-favourable circumstances, even a well-studied non-pathogenic laboratory E. coli strain can exhibit what are considered pathogenic traits.