A probiotic strain (bacillus subtilis DSM 29784, BS29784) is capable of inducing beneficial effects on growth performance and could be therefore a reliable alternative to antibiotic growth promoters. The underlying mechanisms of probiotics, however, are often not fully understood. An in vivo investigation of microbiota profile aimed to observe a positive effect of BS29784 on butyrate producer bacterium such as Ruminococcus or Lachnoclostridium. An in vitro approach, using Caco-2 cells line, showed a decrease of pro-inflammatory compounds (IL8, iNOS) following the supplementation of BS29784. This was mainly explained by an activation of the NFkB pathway. Finally, we also demonstrated the positive correlation of tight junction gene expression with TransEpithelial Electrical Resistance, a sensitive indicator of barrier tissue integrity. In the present study, we used a two-step approach to identify major metabolites produced by BS29784 known to have beneficial effects on broiler performance and health. The first step consisted in cultures of the BS29784 grown in Luria-Bertani and Tryptic Soy Broth culture media. After 4h, 10h and 24h, the supernatant of cultures was analysed with UPLC/MS to identify the metabolites produced in vitro. The second step was an in vivo study, in which 1-day old broiler chicks were continuously administered BS29784 via the diet. At d13, intestinal samples from different locations were collected and analysed for a targeted metabolite analysis. A DNA extraction was performed on the intestinal samples to determine the relative abundance of Bacillus species in different intestinal locations (via qPCR). Nicotinic acid and hypoxanthine were the two main metabolites that were increased in the supernatant of BS29784 cultures. An increase in their concentrations was also measured in ileum and jejunum samples of 13-day old chickens to which the strain was administered. The wound healing assay confirmed the beneficial effect of these two metabolites on barrier function.
Keywords: B. subtilis, chicken, microbiota, inflammation, metabolite