Unveiling the Molecular Characteristics and In Vitro Probiotic Potential of Isolated Lactic Acid Bacteria from Intestine of Freshwater Channa punctata (Taki) and Anabas cobojius (Koi) in Bangladesh

This study investigated the probiotic potential of lactic acid bacteria (LAB) isolated from the intestines of wild freshwater fishes, Channa punctata (Taki) and Anabas cobojius (Koi), collected from Benai Beel of Tangail district, Bangladesh. A total of 24 LAB isolates were obtained and characterized using morphological, biochemical, and molecular approaches, including 16S rRNA gene sequencing. Among these, Lactococcus garvieae (KA6) demonstrated promising probiotic traits. The strain exhibited robust tolerance to acidic pH (as low as pH 3), high bile salt concentration (1%), and elevated NaCl levels (up to 9%), indicating strong survivability in gastrointestinal conditions. KA6 also showed high cell surface hydrophobicity (36%), strong auto-aggregation (85%), and co-aggregation (78% with Staphylococcus aureus ), supporting its potential for intestinal adhesion and pathogen exclusion. Enzymatic assays revealed cellulase activity, suggesting a role in enhancing host digestion and nutrient utilization. The isolate was non-hemolytic, indicating safety, and displayed susceptibility to most tested antibiotics, though antimicrobial activity against selected pathogens ( Staphylococcus aureus , Escherichia coli , or Salmonella typhi ) was absent. These findings highlight Lactococcus garvieae as a potential probiotic candidate for aquaculture, capable of surviving gastrointestinal stress, adhering to intestinal surfaces, and contributing to host nutrition without exhibiting hemolytic activity. So, the survival capacity, adhesion properties, enzymatic activity, and non-hemolytic activity suggest that KA6 can be a strong candidate for probiotic enriched feed development in aquaculture. However, further studies on virulence factors, in vivo efficacy, and safety are recommended to validate its applications in different sectors for sustainable development.