Molecular and Phenotypic Characterization of Lactobacillus delbrueckii subsp. bulgaricus with Antimicrobial Properties as a Potential Probiotic and Postbiotic

Milk and milk products are very well known sources of lactobacilli. The aim of this study was to iso¬late and identify Lactobacillus delbrueckii strains from milk samples by using biochemical and molecular PCR method, and to evaluate their antibacterial effect against pathogenic bacteria. A total of 50 samples of cow's and sheep's milk were collected from local suppliers in Tabriz region, from which 124 different colonies were isolated. To identify the lactobacillus genus and L. delbrueckii species, morphological and biochemical and molecular methods were applied. For antimicrobial activity of the isolates, the disc diffu¬sion assay was used. Of 124 different colonies, 21 isolates were identified as lactobacillus strains. Based on a biochemical method, 3 strains were reported as L. delbrueckii, 7 strains as L. plantarum, 5 strains were L. casei, 3 strains L. acidophilus, and 3 strains were identified as L. rhamnosus. A molecular method based on amplification of the 16S rRNA gene confirmed the presence of 3 strains of L. delbrueckii. According to studies conducted by other researchers, the presence of Lactobacillus delbrueckii subsp. bulgaricus in milk samples is very limited, but in the present study the presence of this microorganism was confirmed by biochemical and PCR molecular methods on cow's and sheep's milk. These isolates had antimicrobial activity against Salmonella typhi ATCC 19430 and Escherchia coli ATCC 25922, and no activity against Staphylococcus aureus ATCC 25923. Based on these results, Lactobacillus delbrueckii subsp. bulgaricus strains have the potential to be used as probiotic bacteria and as food supplements.