Effect of a synbiotic yogurt on levels of fecal bifidobacteria, clostridia, and enterobacteria

Abstract

While ingestion of synbiotic yogurts containing Bifidobacterium animalis subsp. lactis and inulin is increasing, their effect on certain microbial groups in the human intestine is unclear. To further investigate this, a large-scale, crossover-design, placebo-controlled study was utilized to evaluate the effect of a synbiotic yogurt containing B. animalis subsp. lactis Bb-12 and inulin on the human intestinal bifidobacteria, clostridia, and enterobacteria. Fecal samples were collected at 14 time points from 46 volunteers who completed the study, and changes in the intestinal bacterial levels were monitored using real-time PCR. Strain Bb-12 could not be detected in feces after 2 weeks of washout. A live/dead PCR procedure indicated that the Bb-12 strain detected in the fecal samples was alive. A significant increase (P < 0.001) in the total bifidobacterial numbers was seen in both groups of subjects during the final washout period compared to the prefeeding period. This increase in total bifidobacteria corresponded with a significant decrease (P < 0.05) in numbers of clostridia but not enterobacteria. No significant differences in numbers of bifidobacteria, clostridia, or enterobacteria were observed between the probiotic and placebo groups during any of the feeding periods. However, subgrouping subjects based on lower initial bifidobacterial numbers or higher initial clostridial numbers did show corresponding significant differences between the synbiotic yogurt and placebo groups. This was not observed for a subgroup with higher initial enterobacterial numbers. While this synbiotic yogurt can increase bifidobacterial numbers and decrease clostridial numbers (but not enterobacterial numbers) in some individuals, it cannot modulate these microbial groups in the majority of individuals.

Fig 1

Representation of the study design and fecal collection. The study was divided into 5 periods: a prefeeding period, a feeding period, a washout period, a crossover feeding period, and a final washout period. Fecal samples are represented by the sterile tubes containing buffer and collection spoon given to subjects.

Fig 2

C_T standard curves for real-time PCR quantitative analysis of B. animalis subsp. lactis Bb-12, total bifidobacteria, clostridia, and enterobacteria.

Fig 3

Mean numbers of total bifidobacteria for all group A subjects who consumed probiotic first and all group B subjects who consumed placebo first at different time points during the study.

Fig 4

Fecal bifidobacterial levels in subjects subgrouped on the basis of bacterial numbers < 10⁸ CFU/g in the prefeeding period. Period 1, prefeeding period; period 2, first supplemented yogurt feeding period; period 3, first washout period; period 4, crossover feeding period; period 5, final washout period. Group A is represented by the darker shading. P values represent differences between the yogurt feeding and final washout periods compared to the prefeeding period.

Fig 5

Mean numbers of Clostridium cluster I for all group A subjects who consumed probiotic first and all group B subjects who consumed placebo first at different time points during the study. Values below the level of detection (10² CFU/g) have been equated to the value of the limit of detection of 10² CFU/g for mean calculations. The bars represent standard errors.

Fig 6

Fecal Clostridium (cluster I) levels in subjects subgrouped on the basis of bacterial numbers > 3.5 log₁₀ CFU/g in the prefeeding period. Period 1, prefeeding period; period 2, first supplemented yogurt feeding period; period 3, first washout period; period 4, crossover feeding period; period 5, final washout period. Group A is represented by the darker shading. P values represent differences between the yogurt feeding and final washout periods compared to the prefeeding period.

Fig 7

Mean numbers of enterobacteria for all group A subjects who consumed probiotic first and all group B subjects who consumed placebo first at different time points during the study. Values below the level of detection (10³ CFU/g) have been equated to the value of the limit of detection of 10³ CFU/g for mean calculations. The bars represent standard errors.

Fig 8

Fecal enterobacterial levels in subjects subgrouped on the basis of bacterial numbers > 5.5 log₁₀ CFU/g in the prefeeding period. Period 1, prefeeding period; period 2, first supplemented yogurt feeding period; period 3, first washout period; period 4, crossover feeding period; period 5, final washout period. Group A is represented by the darker shading. P values represent differences between the yogurt feeding and final washout periods compared to the prefeeding period.