The Roles of the Host and the Pathogens in Urinary Tract Infections

The severity of urinary tract infections (UTIs) varies depending on the balance between the virulence of the infecting bacterial strain and the antibacterial host defense. Bacterial virulence is determined by a complex of factors in which bacterial adherence to the uroepithelium is the most important virulence factor, in addition to the production of toxins and the formation of biofilm. In immunocompromised patients and in patients with severely dysfunctional urinary tracts, however, the importance of bacterial virulence factors to cause symptomatic infection is decreased or nullified. The antibacterial host defense in the urinary tract depends mainly on native immunity and inflammation. Specific immunity, with antigen presentation and antibody production, does not play an important role in acute UTI. Recent research has provided a deeper understanding of the inflammation process in UTI and demonstrated that the individual variation of UTI susceptibility and renal damage not only depends on urinary tract dysfunctions but is also influenced by genetic polymorphisms in innate immune receptors and signaling proteins, crucial for the innate antibacterial defenses. The identification of these molecular mechanisms in UTI pathogenesis is an important focus for future research aimed at the development of novel nonantibiotic therapies. Patient summary: The severity of urinary tract infections (UTIs) varies depending on the balance between the infecting bacterial strain and the antibacterial host defense. Bacterial virulence is determined by different virulence factors that enhance bacterial persistence and tissue damage. The susceptibility to an UTI is influenced by dysfunctions of the urinary tract and by genetic mechanisms that control the innate immune response to infections. The severity of urinary tract infections (UTIs) varies depending on the balance between the infecting bacterial strain and the antibacterial host defense. Urologists will need a more microbiology- and immunology-centered perspective to successfully manage the increasing threat of UTIs.