Traditional Bulgarian Fermented Foods as a Source of Beneficial Lactic Acid Bacteria.

BACKGROUND

Traditional Bulgarian fermented foods are prominent for their uniqueness of local ingredients, production methods, and endemic microbial species. The present research investigated the diversity and beneficial biological potential of lactic acid bacteria (LAB) isolated from various types of unique Bulgarian fermented foods.

METHODS

Species identification was performed via 16S rDNA sequencing. Biological activity was evaluated by determining antibacterial activity (via agar well diffusion assay), H2O2 production, spectrophotometrically determined auto- and co-aggregation, microbial adhesion to hydrocarbon, and biofilm formation. The biosafety of the isolated lactic acid bacteria was established based on hemolytic activity and phenotypic and genotypic antibiotic susceptibility.

RESULTS

Forty-five strains were isolated from fermented foods (sauerkraut, fermented green tomatoes, fermented cucumbers, kefir, white cheese, and Izvara (curdled milk)). Five species were detected: , , , , and . The most prominent species was , at 47%. For the first time, and , isolated from unique Bulgarian fermented foods, are reported in this study. The antibacterial effect of the cell-free supernatants was evaluated. An antagonistic effect was observed against (57%) and subsp. serotype Enteritidis (19%) for several strains. Only one (Sauerkraut, S15) strain showed activity against . The best autoaggregation ability at hour 4 was observed for (fermented cucumbers, FC4) (48%) and S2 (44%). The highest percentage of co-aggregation with at hou 4 in the experiments, was observed for strains (fermented green tomato, FGT1) (70%), strains S2 (54%), S13 (51%), and S6 (50%), while at hour 24 for strains FGT1 (95%), (Kefir, K7) (89%), S2 (72%), and FC2 (70%). Seven of the isolated LAB strains showed hydrophobicity above 40%. Our results showed that the ability of biofilm formation is strain-dependent. No hemolytic activity was detected. The antibiotic resistance to 10 antibiotics from different groups was tested phenotypically and genotypically. No amplification products were observed in any strains, confirming that the isolates did not carry antibiotic-resistance genes.

CONCLUSIONS

Traditional fermented Bulgarian foods can be considered functional foods and beneficial LAB sources.