Abstract
Lactobacillus paracasei F19 is an emerging probiotic strain that shows considerable promise for use in functional foods for intestinal health. In a multicentre European research project, human feeding trials provided an insight into the ability of this strain to survive gastric transit and transiently colonize the human intestinal tract. Analysis of the faecal microbiota in healthy human volunteers showed that a proportion of the subjects carried a strain indistinguishable from L. paracasei F19 naturally within their intestines. When consumed in different foods, L. paracasei F19 survived gastric transit in healthy infants, adults, and elderly subjects. The bacterium transiently colonized both the colonic lumen and mucosa. Molecular analysis of faecal and colonic biopsy samples from children fed the probiotic showed that L. paracasei F19 did not perturb the population dynamics of other major populations of bacteria in the intestinal microbiota. This strain was well tolerated by young children, healthy adults, adults with milk-hypersensitivity and elderly subjects infected with Helicobacter pylori.