Survival and Impact on Microbial Diversity of Lacticaseibacillus paracasei DG in a Simulation of Human Intestinal Microbial Ecosystem

<b>Background/Objectives:</b> The probiotic <i>Lacticaseibacillus paracasei</i> DG (LpDG) has shown promising results for various gastrointestinal diseases. This study evaluated the survival, metabolic activity, and impact on colonic microbiota of LpDG in an in vitro gastrointestinal tract simulation. <b>Methods:</b> Encapsulated LpDG was tested under simulated fed, fasted, and shortened fasted conditions compared with a blank control in a modified Simulator of the Human Intestinal Microbial Ecosystem (SHIME^®) reactor. Capsule integrity, and cell culturability and viability were assessed at the end of each digestion phase. Metabolic activity (pH, total gas production, and concentrations of short-chain fatty acids, lactate, and ammonium) was assessed after a 24 h colonic incubation with a faecal inoculum. The impact of LpDG on the colonic microbial community was analysed by quantitative polymerase chain reaction and shallow shotgun sequencing. <b>Results:</b> The capsule was completely degraded at the end of the jejunum under all conditions. A low pH had a minimal impact on LpDG culturability and viability. Compared with blank control, LpDG remained metabolically active in the microbial community following a 24 h colonic incubation (LpDG [0-24 h] vs. blank control [0-24 h]: ΔpH, decreased [0.29-0.38 vs. 0.12-0.34]; Δlactic acid, decreased [1.52-1.69 mM vs. 0.13-0.21 mM]; and Δbutyrate, increased [7.49-10.52 mM vs. 5.19-7.76 mM]). Under fed conditions, treatment with LpDG compared with blank control significantly decreased levels of <i>Escherichia coli</i> and <i>Blautia wexlerae</i> and increased Clostridiaceae, Eubacteriaceae, and Lachnospiraceae. <b>Conclusions:</b> LpDG remains viable and metabolically active in the gastrointestinal tract, positively affecting intestinal microbiota and metabolite production.