This study tests the following hypothesis: Does induced asymptomatic bacteriuria (E. coli 83972) protect against symptomatic urinary tract infections in individuals with bladder emptying dysfunctions and prone to recurrent infection episodes? The study is performed using a double-blind randomized study protocol with a cross-over, with re-inoculations being patient-blinded (phase 1). After patients have fulfilled the cross-over, those who have had bacteriuria or placebo-periods < 12 months will be subjected to additional patient blinded inoculations (phase 2). During the entire study (phase 1+2) the study-team and the patients are unaware of urine culture results.