In Vitro Probiotic Attributes of Potential Probiotic Bacillus Strain Isolated from Indigenous Fermented Soybean Foods of Northeast, India

This study aimed to isolate Bacillus species from indigenous non-salted fermented soybean of Northeast India to select a potential novel probiotic candidate. A total of 150 isolates were obtained and identified as Bacillus sp. from hawaijar (109) and kinema (41) based on phenotypic characterization. Antimicrobial activity was evaluated against the five pathogens such as Salmonella enterica typhimurium MTCC 98, Klebsiella pneumoniae MTCC 109, Shigella flexneri MTCC 1457, Pseudomonas aeruginosa MTCC 741, and Escherichia coli (clinical isolates). Forty five Bacillus isolates showed antagonism to at least 3 pathogens. In the antioxidant assay, the Bacillus isolates displayed varying degrees of scavenging activity which were in the range of 37.5–89.6%. In the hydrophobicity and autoaggregation tests, marked differences in cell hydrophobicity to xylene and auto-aggregation, ranging from 3.2 to 79.2% and from 34 to 97%, respectively, were noted among the tested strains. The most of the isolates revealed susceptibility to antibiotics except for nalidixic acid. In the hemolysis test, hemolytic strains were discarded and non-haemolytic strains were used for the in vitro test. Twenty five strains produced exopolysaccharides. In adhesion to Caco-2 cells, all the tested strains showed adhesion but with variation, Bacillus subtilis strain Kak2a showed the highest adhesion (2.34%). Based on the in vitro test, the best three isolates such as Pis3, Kak2a, and, Kw3 were selected as potential probiotics candidates. 16S rRNA sequence analyses were performed to confirm the identity of the selected three Bacillus isolates.