Short-term daily intake of 6 billion live probiotic cells can be insufficient in healthy adults to modulate the intestinal bifidobacteria and lactobacilli

Most intervention studies on probiotics or prebiotics consist of several-week feeding periods and focus on specific host dysfunctions. However, probiotics are often consumed by healthy people and time can be limited; the efficacy of such dietary intervention, however, has only rarely been considered. In this paper, we report the results of a short-term (1 week) study, in which 11 healthy subjects consumed a commercial probiotic food supplement, resulting in a daily intake of about 6 billion viable cells of 10 bacterial species. We measured by quantitative real-time PCR (qPCR) the impact that this product had on faecal Bifidobacterium and Lactobacillus spp. Faecal lactobacilli and bifidobacteria, whose number in the gut is a commonly considered parameter to assess the efficacy of a probiotic/prebiotic intervention, were not significantly affected by the intervention. The only significant increase was observed for intestinal Lactobacillus acidophilus group. However, the significance of this change disappeared after only few days, indicating that it was plausibly due to DNA carryover from the ingestion of a large number of L. acidophilus cells. According to this study, short-term intake of a quite high number of live probiotics can be ineffective in healthy humans on the faecal concentration of bifidobacteria and lactobacilli.