Multifaceted toxin profile of Bacillus probiotic in newly isolated Bacillus spp. from soil rhizosphere

Abstract

Probiotic bacteria mainly Lactic Acid Bacteria (LAB) demonstrate to equilibrate the intestinal microflora. Strains of the Bacillus species have been extensively used as probiotics for human beings, animal feed as well as plant promoting bacteria. Attempts were made to characterize and assess the safety of Bacillus strains for their putative virulence factors. The present study includes screening the isolates by hemolysis on blood agar, DNase, lecithinase and cytotoxic activity as well as detection of toxins in the culture medium. PCR technique was used to detect genes encoding enterotoxin T (bceT), cytotoxin K (CytK), enterotoxin FM (EntFM), non-hemolytic enterotoxin (NheA, NheB), haemolysin BL (HblA, HblC, HblD) and emetic toxin (ces). Among seven Bacillus isolates, only isolates B. cereus sp. M14, B. subtilis sp. M12 and B. methylotrophicus sp. M8 showed weak hemolysis on blood agar. DNase and lecithinase activity were not observed for all isolates. However, isolates B. subtilis sp. M12 and B. cereus sp. M14 indicated low cytotoxic effects on HepG2 cell line. Using two commercial immunoassay kits, no enterotoxin was detected for all isolates. Nhe and Hbl genes were detected in isolates B. methylotrophicus sp. M8 and B. cereus sp. M14, respectively. In contrast, none of the Bacillus isolates harbored bceT, entFM and ces genes in their chromosomes. Taking together, among the evaluated Bacillus isolates, strains B. pumilus sp. M17 and B. pumilus sp. S10 found to be the most promising candidates to fulfill the safety assessments of putative virulence factors suitable for human consumption.