The FOSs stimulate Bifidobacteria l growth and suppress the growth of potentially harmful species in the colon [83]. Other effects of FOS include a decrease in fecal pH, an increase in fecal or colonic organic acids, a decrease in fecal bacterial enzymatic activities and a modification in fecal neutral sterols [83].h e vaginal and fecal fl ora of the mother, and also the environment (air and food, for instance) are important sources of bacteria [2]. Aft er approximately 2 years of age the microbial composition resembling that of an adult becomes established [3].