Characterization of Bacillus spp. strains for use as probiotic additives in pig feed

Bacillus spp. are commonly used as probiotic species in the feed industry, however, their benefits need to be confirmed. This study describes a high throughput screening combined with the detailed characterization of endospore-forming bacteria with the aim to identify new Bacillus spp. strains for use as probiotic additives in pig feed. A total of 245 bacterial isolates derived from African fermented food, feces and soil were identified by 16S rRNA gene sequencing and screened for antimicrobial activity and growth in the presence of antibiotics, bile salts and at pH 4.0. Thirty-three Bacillus spp. isolates with the best characteristics were identified by gyrB and rpoB gene sequencing as B. amyloliquefaciens subsp. plantarum, B. amyloliquefaciens subsp. amyloliquefaciens, B. subtilis subsp. subtilis, B. licheniformis, B. mojavensis, B. pumilus and B. megaterium. These isolates were further investigated for their activity against the pathogenic bacteria, antibiotic susceptibility, sporulation rates, biofilm formation and production of glycosyl hydrolytic enzymes. Additionally, ten selected isolates were assessed for heat resistance of spores and the effect on porcine epithelial cells IPEC-J2. Isolates of B. amyloliquefaciens, B. subtilis and B. mojavensis, showed the best overall characteristics and, therefore, potential for usage as probiotic additives in feed. A large number of taxonomically diverse strains made it possible to reveal species and subspecies-specific trends, contributing to our understanding of the probiotic potential of Bacillus species.