The Impact of Fermented Milk Products Containing Bifidobacterium longum BB536 on the Gut Environment: A Randomized Double-Blind Placebo-Controlled Trial

Abstract

Probiotics, particularly those native to the gut microbiota, have a profound influence on the gut environment. In this study, we conducted a randomized placebo-controlled, double-blind, parallel-group comparison trial to investigate the effects of Bifidobacterium longum BB536 (B. longum BB536) on the fecal microbiota and metabolite compositions in healthy individuals. We compared the effects of fermented milk produced solely with Streptococcus thermophiles and Lactobacillus bulgaricus (placebo group) and fermented milk supplemented with B. longum BB536 (BY group). Our findings revealed a significantly greater relative abundance of Faecalibacterium in the BY group than in the placebo group by the 3rd day, a trend that persisted until the end of the trial on the 17th day. Additionally, the BY group presented significantly increased concentrations of tryptophan (Trp), Indole-3-lactic acid, and Indole-3-aldehyde on the 17th day. A significant positive correlation was observed between the relative abundance of Faecalibacterium and the number of viable B. longum BB536 bacteria in the feces. The concentrations of Trp and Indole-3-acetic acid were also significantly correlated with the number of viable B. longum BB536 bacteria in the feces. Our results suggest that B. longum BB536 intake can modulate the gut microbiota and metabolite profiles, which are general indicators for monitoring the gut environment, potentially conferring health benefits to the host.

Keywords: Bifidobacterium longum BB536; Faecalibacterium; gut environment; probiotics; tryptophan; tryptophan metabolites.

Figure 1

Impact of B. longum BB536 bacteria on the fecal microbiota composition: (a) stacked bar graph showing the 20 most abundant genera in the fecal microbiota; (b) the relative abundance of Faecalibacterium in fecal samples; (c) DNA copy number of F. prausnitzii JCM 39207 when cocultured with B. longum BB536 in GAM medium at 37 °C for 24 h. Statistical significance is indicated as follows: $ p < 0.1; * p < 0.05 with (b) Quade’s nonparametric ANCOVA and (c) Student’s t test.

Figure 2

Correlation between fecal metabolite concentrations and viable B. longum BB536 counts: (a) quantitative measurements of fecal Trp, IAA, ILA, IAld, and formic acid concentrations; (b) correlation of the concentrations of the same five metabolites on day 17 and the viable B. longum BB536 count. Statistical significance is indicated as follows: $ p < 0.1; * p < 0.05; with (a) Quade’s nonparametric ANCOVA and (b) Spearman’s correlation.

Figure 3

Heatmap of Spearman’s correlations among Trp metabolites on day 17. The map displays pairwise comparisons of Trp, ILA, IAA, IAld, Indole, Indole-3-propionic acid (IPA), and tryptamine (TAM) on day 17. Statistical significance is indicated as follows: $ p < 0.1; * p < 0.05.

Figure 4

Correlation between alpha diversity of the fecal microbiota and viable B. longum BB536 count. Correlation of preintake fecal microbiota alpha diversity with viable B. longum BB536 count on (a) day 3 and (b) day 17. Alpha diversity was scored by Chao1, Faith’s phylogenetic diversity, observed features, and Pielou’s evenness tests. Statistical significance is indicated as follows: $ p < 0.1; * p < 0.05, with Spearman’s correlation.