Exploring a novel direct-fed microbial for ruminants to mitigate in vitro Salmonella invasion and infection

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Abstract Managing bacterial infections is of great importance in cattle production, particularly those caused by Salmonella enterica serovars Typhimurium or Dublin, which can impact both animal health and human food safety. Direct-fed microbial (DFM) can support gastrointestinal health and alleviate potential bacterial infections. In the present study, the capacity of a bacteria-based DFM product [BOVAMINE DEFEND Plus; BDP; Novonesis, Denmark (BDP)] containing Lactobacillus animalis, Propionibacterium freudenreichii, Bacillus licheniformis, and B. subtilis to reduce Salmonella Typhimurium ATCC14028 invasion was investigated using the HT29-MTX cell line (Exp. 1) and also to evaluate the possible antagonistic effect against S. Dublin using an in vitro agar well diffusion method (Exp. 2). Briefly, in Exp. 1, after a 30 min pre-incubation with 1.0 ×108 CFU of BDP and/or 2.5 × 106 CFU of S. Typhimurium were added to each transwell. The quantity of S. Typhimurium invading the cells was measured after 90 min of co-incubation using CFU counts. As a control, the viability of the total S. Typhimurium was assessed to confirm the mode of action of BDP targets the pathogen invasion properties. In Exp. 2, the antagonistic efficacy of BDP against S. Dublin CHCC41286, isolated from cattle, was tested by adding BDP to wells in CLED agar plates casted with the pathogen above, zones of inhibition measured after 48 h incubation. In Exp. 1, BDP significantly (P < 0.05) reduced by 80.6 % the invasion of S. typhimurium into HT-29-MTX cells as well as from 16 % the viability of the pathogen. The antagonistic properties of BDP towards S. Dublin were confirmed by clear inhibition zones (8.6 mm). These two in vitro findings set the stage for exploring the potential benefits of using a novel DFM as a promising tool and strategy to mitigate Salmonella infections in ruminants and improve animal health, food safety, and public health. Further in vivo confirmation needs to be developed to validate these preliminary in vitro results.