Fermented Rice as a Reservoir of Potential Probiotic Bacteria: Isolation, Identification, and Functional Characterization

Fermented rice, known as ‘Panta Bhat,’ in South Asian countries, is a common dietary staple rich in beneficial bacteria that may have probiotic properties. This research aimed to isolate, identify, and analyze the probiotic characteristics of two bacterial strains from fermented rice. Through 16S rRNA gene sequencing, sequence analysis, and a homology search in the NCBI database, these isolates were identified as Enterococcus durans JCM 8725 and Enterococcus faecium ATCC 19434, showing 98.86% and 98.83% similarity, respectively. The probiotic potential, functional characteristics, safety, and stress tolerance of these strains were assessed in vitro. Both strains demonstrated promising probiotic attributes, including resistance to 0.3% bile salts, robust growth across various salt concentrations (with optimal growth at 1% NaCl, and resilience in acidic pH ranges (with optimum growth at pH 4). In the pepsin tolerance assay, E. durans and E. faecium showed viable counts of 4.544 and 4.158 log CFU/mL, respectively, indicating good survivability under gastrointestinal stress. Both isolates were non-amylolytic, non-hemolytic, and lacked gelatinase activity, indicating a positive safety profile. Antibiotic susceptibility tests revealed that E. durans was responsive to five antibiotics, while E. faecium was sensitive to three. The isolates demonstrate strong antibacterial activity against Bacillus subtilis and Pseudomonas sp., and inhibit biofilm formation in S. aureus, S. flexneri, B. subtilis, and Salmonella sp. Given their favorable functional properties and safety profile, these isolates show promise as probiotics. However, further in vivo and mechanistic studies are required to validate their use in food and pharmaceutical applications.