پریسا فتحی رضایی

BACKGROUND AND OBJECTIVES According to the definitions of the World Health Organization (WHO) and the Food and Agriculture Organization (FAO), probiotics as living microorganisms by maintaining or improving the microbial balance, can confer health benefits on their host. Probiotic bacteria regulate the gut microbiota by adhering to the intestinal epithelial tissues, enhancing nutrient uptake, synthesizing vitamins and short-chain fatty acids, and modulating the pH of the gut. MATERIALS AND METHODS After isolation and purification, probiotic properties of the M20 isolate were evaluated by gram staining, oxidase, catalase, hemolysis, and acid and bile salt resistance tests. Also, microbial tests including nitrate reduction, SIM, sugar fermentation, antibiotic resistance and antimicrobial were conducted. For molecular identification of the isolate, DNA was extracted using a kit, PCR amplification of 16S rRNA gene performed, electrophoresed and phylogenetic tree of the isolate constructed by neighbor-joining method by BioEdit and MEGA version 7 softwares. RESULTS AND DISCUSSION According to the results, the M20 isolate was known as a probiotic bacteria due to grampositive morphology, negative results for catalase and oxidase tests, resistance to bile salts and acidic pH, and absence of hemolysis. The microbial tests indicated that the isolate was resistant to antibiotics and capable of sugar fermentation and nitrate reduction. Based on the molecular identification result, the isolate showed highest genetic similarity (86%) to Lactobacillus plantarum DMS 10667 (T) CP032744. The nucleotide sequence of the M20 isolate has been deposited in the NCBI database under accession number OQ568197. Moreover, the production of asparaginase and glutaminase by the M20 isolate, which are known therapeutic enzymes, was confirmed. CONCLUSION The lactic acid bacteria isolated from traditional Maragheh yogurt exhibited probiotic properties, could be considered as a favorable candidate to