From the anatomical point of view infections of the lower urinary tract and
the pyelonephritis are different diseases, but these kinds of infections a
s well as the asymptomatic bacteriuria are based on an equal pathogenetic b
ackground. The urinary tract does not present optimal living conditions for
all microorganisms. Urine is a medium of changing osmolality containing di
fferent substances (immunoglobulines, Tamm-Horsfall-glykoprotein, polyamine
s) with an bactericidal effect. In case of acute disease and of microorgani
sms persisting in the urinary tract, the adhesion of bacterial strains to t
he cells of the epithelial boundary layer plays an important role for the f
ollowing step of internalization in the uroepithelium. During this process,
the secretion of different cell mediator proteins (IL-6, IL-8, PDGF, TNF-a
lpha) will activate various immunocompetent cell populations. Alterations o
f specific host-defence mechanisms, the expression of receptors for adhesio
n molecules of uropathogens to the surfaces of epithelial cells as well as
anatomical abnormalities of the urinary tract determine the course of a dis
ease. A great number of efficient drugs is available for treating an acute
infection. It is, however, more problematic to decide on the necessity of t
reating cases of asymptomatic bacteriuria as well as to chase adequate drug
s for chronic recurrent or relapsing infections.