Fecal excretion of Bifidobacterium infantis 35624 and changes in fecal microbiota after eight weeks of oral supplementation with encapsulated probiotic.

Certain randomized, placebo-controlled trials of oral supplementation with B. infantis 35624 have demonstrated the amelioration of symptoms of irritable bowel syndrome. Potential GI colonization by B. infantis 35624 or effects of supplementation on resident GI microbiota may pertain to these clinical observations. In this study, fecal excretion of B. infantis 35624 before, during and after 8 weeks of daily treatment was compared in subjects with IBS who received either the encapsulated oral supplement (n = 39) or placebo (n = 37) and in healthy subjects who received the supplement (n = 41). Secondarily, changes in assessed fecal microbiota and IBS symptoms were determined. Supplementation significantly increased fecal B. infantis 35624 excretion vs. placebo in IBS subjects; excretion in healthy subjects receiving supplement was quantitatively similar. Fecal levels of the probiotic declined and approached baseline once dosing ceased, documenting that colonization is transient. Although supplementation increased numbers of B infantis 35624 within the GI tract, limited changes in 10 other fecal taxa were observed either in healthy subjects or those with IBS. No impact on IBS symptoms was observed. Detection of bacterial DNA in fecal samples suggests that the probiotic is able to survive transit through the GI tract, although strain selective culture techniques were not performed to confirm viability of B. infantis 35624 in the feces. Continuous probiotic administration was necessary to maintain steady-state transit. Given the complex spectrum of GI microbiota, however, monitoring perturbations in selected taxa may not be not a useful indicator of probiotic function.