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 (1 ). They have been used in the gastrointestinal tract as capsules or as fermented milks (2 ). The characteristics of the strains proposed as probiotics have been published (3 ) or patented under an elaboration process (4 –6 ). 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 (7 ).