In vitro evaluation of candidate Bacillus spp. for animal feed

Abstract

The aim of this study was to select aerobic spore-formers for animal feed based on their in vitro probiotic potential, including their enzyme-producing ability and safety assessment. Seven isolates out of 187 spore-forming bacteria were selected for their ability to produce cellulase (89.21–1668.32 U/ml), xylanase (1399.68–4351.10 U/ml), and phytase (2.72–28.70 U/ml). Among seven isolates, five had activities towards a broad range of p-nitrophenyl esters with acyl chain lengths from C2 to C12. The probiotic properties of all selected isolates varied with respect to their acid and bile salt tolerance under simulated gastrointestinal tract (GIT) conditions, and their adherence ability to human intestinal cell lines (Caco-2 and HT-29). The safety assessment revealed that the isolate CM40 was not cytotoxic to Caco-2 and HT-29, did not exhibit hemolytic activity, carried no enterotoxin or emetic toxin genes, and was susceptible to ten antibiotics, including six key antibiotics (chloramphenicol, erythromycin, gentamicin, tetracycline, streptomycin, and kanamycin) as recommended by the European Food Safety Authority (EFSA). Co-incubation of isolate CM40 with enteric bacteria (Salmonella Typhi, Salmonella Enteritidis 1781, and Escherichia coli) demonstrated that CM40 significantly decreased the number of pathogens (about 30–48%) adhering to Caco-2 and HT-29 (P < 0.05). Analysis of gene encoding 16S rRNA, gyrase A (gyrA) and the cheA histidine kinase revealed that CM40 belongs to Bacillus subtilis. On the basis of probiotic properties and basic safety aspects, the B. subtilis strain CM40 was found to possess desirable in vitro probiotic properties, and may be a potential candidate for supplementation of animal feed.