Anti-inflammatory gut immune modulation induced by direct-fed endospores of bacteriostatic lipopeptide-producing Bacillus velezensis MFF 2.2 and B. subtilis TC12 in BALB/c mice: A first step toward a probiotic additive to prevent post-weaning diarrhea.

Restrictions on the use of antibiotic growth promoters and the increasing pressure to reduce prophylactic antibiotic use due to rising antimicrobial resistance have intensified the need for safer strategies to prevent post-weaning diarrhea (PWD) in swine. Probiotic Bacillus strains represent a promising alternative because of their resilience, stability, and capacity to modulate gut microbial and immune responses. This study assessed the safety and immunomodulatory effects of endospores from Bacillus velezensis MFF 2.2 and B. subtilis TC 12 in a mouse model, as an initial screening step before conducting trials in the target species. Mice (n = 6 per group) received a daily oral dose of 108 CFU/ml for 10 consecutive days, or saline as control. No signs of toxicity or histopathological alterations were observed. In the small intestine, goblet cell counts and intraepithelial lymphocyte numbers did not differ significantly from controls, and no increases in TNF-α or IFN-γ were detected. However, treated mice showed a significant rise in IL-10 and in the IL-10/IFN-γ ratio. Previous studies demonstrated that lipopeptide extracts (LPE) from MFF 2.2 exert anti-inflammatory and bacteriostatic effects against PWD-associated pathogens. Based on the modest anti-inflammatory response elicited by the endospores, a combined endospore + LPE formulation appears to be the most suitable candidate for future evaluation in swine.