Isolation, Identification and Comparison of Some Properties of Lactobacillus Delbrueckii Subsp. Bulgaricus Strains from Traditional Bulgarian and Italian Yogurts

Abstract

An important step in the development of successful technological schemes for production of yogurt and other functional foods is the selection of appropriate Lactobacillus strains with useful properties that are resistant to antibiotics and bacteriocins. In the present study eleven Lactobacillus strains were isolated from fourteen homemade Bulgarian and Italian yogurts. The isolates were identified as Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) by 16S rDNA sequence analysis. The results from comparative 16S rRNA gene sequence-based phylogenetic analysis revealed 92-99% pairwise similarity of the isolates to the reference L. bulgaricus strains. The antimicrobial activity, antibiotic susceptibility and nisin resistance of the isolated L. bulgaricus strains were examined. Bulgarian L. bulgaricus strains 3-BG, 5-BG and 8-BG were characterized by highest antimicrobial activity against the Gram-positive bacteria Staphylococcus aureus ATCC 25923, Listeria monocytogenes NBIMCC 8632, Listeria ivanovii ATCC 19119, Listeria innocua ATCC 33090, Enterococcus faecalis ATCC 19433 and Enterococcus faecuim ATCC 19434. L. bulgaricus 8-BG was active also against the Gram-negative bacteria Pseudomonas aeruginosa ATCC 9027, Proteus vulgaris ATCC 6380, Salmonella enteritidis ATCC 13076, Salmonella abony NTCC 6017 and Escherichia coli ATCC 25922. In contrast, Italian L. bulgaricus strains demonstrated low antimicrobial activity. Bulgarian L. bulgaricus strains showed moderate sensitivity or resistance to most of the antibiotics used in the screening, while Italian L. bulgaricus strains were sensitive. Bulgarian L. bulgaricus strains 1-BG and 6-BG were resistant to 10 and 13 of a total of 24 antibiotics tested, respectively. Nisin resistance test showed that 10 of a total of 11 L. bulgaricus strains were highly sensitive to nisin (MIC values varying from 0.078 mg/mL to 0.156 mg/mL), except of Italian strain L. bulgaricus 6-IT which was resistant to nisin.