# Gastrointestinal Survivability of a BSH-Positive Lacticaseibacillus rhamnosus VB4 Strain and Its Effect on Bile Acid Deconjugation in a Dynamic In Vitro Gut Model

## TL;DR

This study shows that a BSH-positive Lacticaseibacillus rhamnosus strain survives the gut and helps deconjugate bile acids, suggesting its potential as a probiotic.

## Contribution

The study demonstrates the strain's survivability and bile acid deconjugation under fed conditions using a dynamic in vitro gut model.

## Key findings

- The VB4 strain showed good survivability in the upper gastrointestinal tract.
- The strain sustained bsh gene expression in both the stomach/small intestine and colon.
- VB4 reduced conjugated bile acids in the small intestine and improved deconjugation in the colon.

## Abstract

Background: Bile salt hydrolase (BSH) is a key probiotic trait, as it facilitates both host metabolism and bacterial survival into the gastrointestinal tract (GIT), through bile acid (BA) deconjugation, keeping intestinal homeostasis. Objectives: The present study aims to investigate the viability of the Lacticaseibacillus rhamnosus VB4 strain and its effects on bile acid deconjugation during the gastrointestinal tract (GIT) passage, under a fed condition, using the in vitro SHIME® (Simulator of the Human Intestinal Microbial Ecosystem) model. Methods: Gastric, small intestinal and colonic fractions were monitored and a fecal slurry from a healthy donor was inoculated into the colonic compartment to establish the intestinal microbiota. Samples were collected at the end of stomach, duodenum, jejunum, ileum phases, and colon after 0, 16 and 24 h. Strain survival was assessed by culturing method, and bsh gene expression was revealed by quantitative PCR (qPCR). In addition, UHPLC/HR-MS was performed to reveal the hypothetical changes in BAs profile after strain administration. Results: Good survivability of the VB4 strain in the upper GIT was revealed. Furthermore, VB4-inculated sample showed sustained expression of bsh in both the stomach/small intestine and colon fractions at all sampling times. Analysis of the BAs profile shown that the VB4 strain reduced the levels of the main conjugated BAs in the small intestine under fed condition and improved the deconjugation efficiency during colonic transit compared with the control. Conclusions: These findings highlight the survivability of L. rhamnosus VB4 strain inside the gut and its potential as biotherapeutic BAs-mediator candidate, demonstrating that transcriptomic and metabolomic approaches coupled to a dynamic in vitro gut model represent a robust tool for selection of a BSH-positive probiotic candidate.