Effect of Bacillus subtilis, Enterococcus faecium, and Enterococcus faecalis supernatants on serotonin transporter expression in cells and tissues

BACKGROUND: Bacillus subtilis (B. subtilis), Enterococcus faecium (E. faecium), and Enterococcus faecalis (E. faecalis) are probiotics that are widely used in the clinical treatment of irritable bowel syndrome (IBS). Whether the supernatants of these three probiotics can improve gastrointestinal sensation and movement by regulating the serotonin transporter (SERT) expression needs to be clarified. AIM: To investigate whether B. subtilis, E. faecium, and E. faecalis supernatants can upregulate SERT expression in vitro and in vivo. METHODS: Caco-2 and HT-29 cells were stimulated with probiotic culture supernatants for 12 and 24 h, respectively. A male Sprague-Dawley rat model of post-infectious irritable bowel syndrome (PI-IBS) was established and the rats were treated with phosphate-buffered saline (group A) and three probiotics culture supernatants (groups B, C, and D) for 4 wk. The levels of SERT were detected by quantitative PCR and western blotting. RESULTS: The levels of SERT at post-treatment 12 and 24 h were significantly elevated in Caco-2 cells treated with B. subtilis supernatant compared with those in the control group ((a)P < 0.05). Those levels were markedly upregulated in Caco-2 cells stimulated with E. faecium and E. faecalis supernatants at 24 h ((a)P < 0.05). In addition, SERT expression in groups B, C, and D was significantly higher than that in group A in the 2nd wk ((a)P < 0.05). Increased SERT expression was only found in group D in the 3rd wk ((a)P < 0.05). However, there was no significant difference in SERT expression between the groups in the last week (P > 0.05). CONCLUSION: The supernatants of B. subtilis, E. faecium, and E. faecalis can upregulate SERT expression in intestinal epithelial cells and the intestinal tissues in the rat model of PI-IBS.