Baseline microbiota activity and influence responses to prebiotic initial bifidobacteria counts dosing in healthy subjects

Background Dietary intervention with prebiotics can cause changes in the colonic microbiota and their metabolic activities. Aim To investigate whether the response to prebiotic dosing is influenced by the baseline metabolic activity of the colonic flora and bifidobacteria counts. Methods The 4-week effect of lactulose (10 g bid.; n = 29) and oligofructose-enriched inulin (10 9 bid.; n = 19) was evaluated in healthy human volunteers. Lactose-[N-15, N-15]-ureide was used to study the colonic NH3-metabolism. Urine (48 h) and faeces (72 h) were collected and analysed for p-cresol and N-15-content by gas chromatography-mass spectrometry and isotope ratio mass spectrometer, respectively. Faecal bifidobacteria were quantified by real-time polymerase chain reaction. Results After the 4-week prebiotic administration period, the urinary excretion of p-cresol and N-15 was significantly decreased in both groups (P < 0.05) corresponding to a significantly higher faecal excretion of N-15 (P < 0.05). The decrease in urinary 15 N and p-cresol excretion significantly correlated with baseline 15 N and p-cresol levels (P < 0.05), indicating that subjects with higher baseline levels showed a higher response to prebiotic dosing. Furthermore, a significant correlation was seen between baseline bifidobacteria counts and the effect of prebiotic intake (P < 0.05). Conclusion The response to prebiotic dosing, as indicated by the fate of NH3, p-creSol and bifidobacteria, is determined by the initial colonic conditions.