[Nephrology-part 3: Urinary tract infections].

Urinary tract infections are one of the most common bacterial infectious diseases in humans. Depending on the localization and the effectiveness of pathogenetic factors, various clinical pictures (lower urinary tract infection, pyelonephritis, asymptomatic bacteriuria) have to be differentiated. There are virulence factors of microorganisms on the one hand and defense mechanisms on the other, which influence the manifestation and the course of disease. The process of bacterial attachment to the epithelial cells of the boundary layer, the internalization and invasion of bacteria could be important for acute and chronic disease. Disturbances of local defense mechanisms, such as increased urinary glucose concentration in diabetes or variations of Tamm-Horsfall protein and defensin levels, may influence the course of infection. On the basis of microbiological and laboratory findings as well as the results of clinical and ultrasound procedures, the decision on the therapeutic strategy should be made. There are different treatment recommendations for acute uncomplicated and complicated cases as well as for chronic diseases. Future investigations should focus on effective therapeutic options for special immunocompromised patients in relation to the microbiological aspects and defense mechanisms of the host.