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),
HO 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:
Lactiplantibacillus plantarum, Levilactobacillus koreensis,
Levilactobacillus brevis, Lactobacillus helveticus, and
Levilactobacillus yonginensis. The most prominent species was L.
plantarum, at 47%. For the first time, L. koreensis and L.
yonginensis, 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 Escherichia coli (57%) and
Salmonella enterica subsp. enterica serotype Enteritidis (19%)
for several L. plantarum strains. Only one L. brevis
(Sauerkraut, S15) strain showed activity against E. coli. The best
autoaggregation ability at hour 4 was observed for L. koreensis
(fermented cucumbers, FC4) (48%) and L. brevis S2 (44%). The highest
percentage of co-aggregation with Candida albicans, at hou 4 in the
experiments, was observed for strains L. koreensis (fermented green
tomato, FGT1) (70%), L. plantarum strains S2 (54%), S13 (51%), and S6
(50%), while at hour 24 for strains L. koreensis FGT1 (95%),
L. brevis (Kefir, K7) (89%), L. plantarum S2 (72%), and
L. koreensis 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.