Extra-intestinal E. coli (ExPEC) may transition from benign colonization of the enteric and vaginal tracts to cause urinary tract infections (UTIs), septicemia, and meningitis. ExPEC colonization of the lower urinary tract leads to an acute infection of the superficial bladder urothelial cells, termed cystitis. Notably, 50% of all women will experience at least one UTI during their lifetime. Even though ExPEC UTI induces a robust innate immune response, 25% of women with acute cystitis experience a second UTI within 6 months. This failure to mount a protective immune response may be due to host genetic factors, antibiotic use, heterogeneity among ExPEC strains, active suppression of innate and adaptive immunity by ExPEC, and the ability of ExPEC to reside within protected, quiescent reservoirs.
This review highlights the different stages of the ExPEC developmental cycle in the host bladder tissue, and describes the strategies employed by both players to gain the upper hand.