Lactobacillus helveticus-derived postbiotic and live Saccharomyces boulardii restore gut microbiota after antibiotic disturbance in an in vitro canine gut model.

Gut microbiota plays a central role in dog health, supporting nutritional and physiological processes. However, antibiotic treatment can disturb microbiota equilibrium, leading to a perturbated state, called dysbiosis. While probiotic and postbiotic strategies are increasingly studied, their use in dogs remains poorly documented, particularly in the context of antibiotic-induced dysbiosis. In this study, we provide novel insights by evaluating for the first time, the efficacy of two microbiota restoration strategies using a canine-specific in vitro gut model (Canine Mucosal Artificial Colon, CANIM-ARCOL): the probiotic live yeast Saccharomyces boulardii CNCM I-1079 and the postbiotic heat-inactivated Lactobacillus helveticus HA-122. Both were administered at in-field doses twice a day, during and after a 5-day antibiotic treatment (metronidazole/enrofloxacin), to assess their ability to enhance microbiota resistance and/or promote recovery in both lumen and mucus-associated microbiota. Our results demonstrated that within two days post-antibiotic treatment, both interventions significantly mitigated the bloom of Enterobacteriaceae (up to -75% relative abundance, P < 0.05), accelerated the recovery of total bacterial load (increase of ∼1.5 log 10 copies/ml), and promoted a faster restoration of bacterial diversity (Shannon index returning to baseline by day 14 vs day 16 in the control). Additionally, S. boulardii significantly reduced redox potential (+200 mV with antibiotic vs only +80 mV with yeast, P < 0.0001), while L. helveticus preserved short-chain fatty acid concentrations (>100 mM vs 80 mM under control conditions) and upregulated beneficial metabolic pathways (e.g. norspermidine biosynthesis). Moreover, both treatments reduced variability in microbiota profiles and enhanced functional resilience post-antibiotic exposure. These findings provide compelling evidence supporting the relevance of probiotic and postbiotic strategies in companion animal and highlight the potential of the CANIM-ARCOL model as an ethical and robust alternative to in vivo trials for preclinical evaluation of microbiota-targeted intervention in canine nutrition and health.