16S-Amplified Ribosomal DNA Restriction Analysis Assay for Discriminating Potentially Probiotic Lactobacillus Species Isolated from Traditional Dairy Products

Background: Traditional dairy products are the main sources for probiotic bacteria. This study aimed to isolate and characterize the potentially probiotic Lactobacillus strains isolated from traditional dairy products in Iran. Methods: Microbial population of each dairy product was enriched and screened for acid- and bile- resistant strains. The isolates were primarily characterized by conventional phenotypic and biochemical tests. The species were finally identified using restriction analysis and 16S rDNA sequencing. In addition, the antibacterial activity of the four most common species was evaluated against seven gastrointestinal pathogens. Results: From a total of nine yogurt and cheese samples, 17 acid-resistant Lactobacillus strains were isolated (survival>50% in PBS buffer, pH 2.5 for 3 h). Eight of them also showed high tolerance to bile. Also, the superiority of molecular techniques over phenotypic tests for effective identification of species was observed. Biochemical tests were useful in combination with 16S-amplified ribosomal DNA restriction analysis (ARDRA) technique to discriminate the isolates at species level. Conclusion: 16S–ARDRA in combination with biochemical tests is suggested as a potentially useful method for accurate identification of Lactobacillus species where the 16S-rDNA sequencing could not discriminate between two closely related species. Considering the acid and bile resistance capacity of isolated strains, traditional dairy products may be used as important sources of probiotic strains.