Effects of estrogen administration on the colonization capability of lactobacilli and Escherichia coli in the urinary tracts of mice.

The use of probiotic microorganisms has been widely promoted in the last 20 yr. They have been used in the gastrointestinal tract as capsules or as fermented milks. The characteristics of the strains proposed as probiotics have been published or patented under an elaboration process. The first step in designing a probiotic product is to isolate and characterize strains with some beneficial properties. The second step is to determine the optimal conditions to obtain the highest amount of viable microorganisms, together with the study of the best conditions to produce antagonistic substances. Urinary tract infections (UTIs) constitute a common cause of illness in pre- and postmenopausal women. It was estimated that 40-50% of adult women suffer a cystitis during their life. Ninety percent of acquired ambulatory UTIs and 30% of nosocomial infections are produced by Escherichia coli. The healthy human urinary tract is free of microorganisms, except for the anterior urethra, which is colonized by indigenous microbiota. The vaginal environment is a dynamic and complex ecological system with a highly heterogeneous microflora; thus favorable conditions exist for the colonization process, which is also affected by factors external to the tissues. The distal urethra and periurethral areas are separated ecological niches, both covered by the vaginal secretions that contain approx 109 microorganisms/mL. In these secretions, members of the genus Lactobacillus are predominant. Bacterial colonization does not increase because of the urinary flux, which clears the bacterial cells from the outer surfaces, as well as other factors such as pH, osmolarity, and urea concentration.