Baby-SPIME: A dynamic in vitro piglet model mimicking gut microbiota during the weaning process.

The study aimed to adapt the SHIME(R) model, developed to simulate human digestion and fermentation, to a baby-SPIME (baby Simulator of Pig Intestinal Microbial Ecosystem). What constitutes a unique feature of this model is its twofold objective of introducing an ileal microbial community and mimicking a dietary weaning transition. This model should then be ideally suited to test the dietary weaning strategies of piglets in vitro. Regarding the microbiota, the main phyla making up the model were Firmicutes, Bacteroidetes and Proteobacteria although Bacteroidetes decreased after inoculation (p=0.043 in ileum, p=0.021 in colon) and Delta-Proteobacteria were favoured (p=0.083 in ileum, p=0.043 in colon) compared to Gamma-Proteobacteria. The designed model led to a low representation of Bacilli - especially Lactobacillus sp. in the ileum and a weak representation of Bacteroidia in the proximal colon. However, Mitsuokella and Prevotella were part of the major genera of the model along with Bifidobacterium, Fusobacterium, Megasphaera and Bacteroides. As a result of weaning, two major changes - normally occurring in vivo - were detected in the system: firstly, Firmicutes diminished when Bacteroidetes increased particularly in the proximal colon; secondly, Bacteroides decreased and Prevotella increased (mean value for four runs). In terms of metabolite production, while a ratio acetate: propionate: butyrate of 60:26:14 was obtained in post-weaned colon, the expected inversion of the ratio propionate: butyrate in the post-weaned ileum was unfortunately not observed. To conclude, the so-called baby-SPIME model meets expectations regarding the resident microbiota of the proximal colon bioreactor and the metabolites produced thereof. In terms of the evolution of major groups of bacteria, the in vitro weaning process appeared to be successful. However, higher concentration of butyric acid would have been expected in ileum part of newly weaned piglets, as observed in vivo. The microbiota in the ileum bioreactor seemed in fact to act like a pre-colon. This suggests that microbial profile in ileum bioreactor had to be improved