The colonisation and establishment of the intestinal microbiota starts immediately at birth and is essential for the development of the intestine and the immune system. This microbial community gradually increases in number and diversity until the age of two or three years when it becomes a stable ecosystem resembling that of adults. This period constitutes a unique window of opportunity to modulate it through probiotic action, with a potential impact in later health. In the present work we have investigated how putative bifidobacterial probiotics modify the metabolic profiles and immune-modulatory properties of faecal microbiotas. An in vitro pH-controlled single-stage continuous-culture system (CCS) inoculated with infant faeces was employed to characterise the effects of two Bifidobacterium species on the intestinal microbiotas in three children, together with the effects of these modified microbiotas on cytokine production by HT-29 cells. Intestinal bacterial communities, production of short-chain fatty acids and lactate were determined by quantitative PCR and gas chromatography, respectively. Cytokines production by HT-29 cells was measured by ELISA. The combination of CCS with infant faeces and human intestinal cells provided a suitable model to evaluate the specific modulation of the intestinal microbiota and immune system by probiotics. In the CCS, infant faecal microbiotas were influenced by the addition of bifidobacteria, resulting in changes in their ability to induce the production of immune mediators by HT-29 cells. The different metabolic and immunological responses induced by the bifidobacterial species tested indicate the need to assess potential probiotics in model systems including complex intestinal microbiotas. Potential probiotic bifidobacteria can modulate the infant microbiota and its ability to induce the production of mediators of the immune response by intestinal cells.
Keywords: Bifidobacterium; cytokines; faecal microbiota; infants; probiotic.