Biodiversity of the bacteriocinogenic lactic acid bacteria isolated from boza ? from isolation to application

LEBLANC, J, G.; FAVARO, L.; TODOROV, S. D.

Clermont-Ferrand

Congreso; 18ème Colloque du Club des Bactéries Lactiques; 2012

18ème Colloque du Club des Bactéries Lactiques

The aim of this study was to isolate new bacteriocin-producing lactic acid bacteria from boza and to compare the bacteriocins with those previously described for strains isolated from the same niche. Boza is a low-alcohol beverage produced from the fermentation of barley, oats, millet, maize, wheat or rice. Cooked cereal is strained to remove most of the solids, sugar is added to taste and inoculated with a starter culture, either yogurt or sourdough. By definition, bacteriocins produced by lactic acid bacteria are proteinaceous antibacterial compounds that exhibit bactericidal or bacteriostatic activity against genetically closely related bacteria. Bacteriocins are generally low molecular weight proteins that gain entry into target cells by binding to cell surface receptors. Their bactericidal mechanism may vary and may include pore formation, degradation of cellular DNA, disruption through specific cleavage of 16S rDNA, and inhibition of peptidoglican syntesis. Five bacteriocin-producing lactic acid bacteria [Lactobacillus plantarum ST69BZ (3.2kDa), Enterococcus faecium ST62BZ (10.0 kDa) and Leuconostoc lactis ST63BZ (10.0 kDa), ST611BZ (3.2 kDa) and ST612BZ (6.5 kDa)] were isolated from boza. The bacteriocins of all five isolates inhibited the growth of Enterococcus spp., Escherichia coli, Klebsiella pneumoniae, Lactobacillus spp., Lactococcus lactis subsp. lactis, Listeria spp., Pseudomonas aerouginosa, Staphylococcus spp. and Streptococcus caprinus. The highest levels of bacteriocins ST69BZ (12 800 AU/ml), ST62BZ (25 600 AU/ml), ST63BZ (1 600 AU/ml), ST611BZ (52 600 AU/ml) and ST612BZ (25 600 AU/ml) were recoded after 24 h of incubation at 30oC. The antimicrobial activity of all five bacteriocins was inhibited after treatment of the cell-free supernatants with proteolotic enzymes. Treatment of the cell-free supernatant containing bacteriocin ST63BZ with alpha-amylase resulted in loss of antibacterial activity. All five bacteriocins remained active after incubation at pH 2.0 to 8.0. A decrease in bacteriocin ST612BZ activity was recorded after 60 and 120 min at 100ºC. Surfactants had no effect on the activity of the four bacteriocins. Addition of Triton X-114 to bacteriocins ST69BZ and ST62BZ led to decreased activity. Addition of 1.0, 2.0 or 5.0 mM EDTA (final concentrations) to the 5 bacteriocins did not affect their activity. The mode of activity of bacteriocins ST69BZ, ST626BZ, ST6311BZ, ST611BZ and ST612BZ is bactericidal, as determined against Enterococcus faecium HKLHS and Lactobacillus sakei DSM 20017, respectively. Enterococcus faecium HKLHS and Lactobacillus sakei DSM 20017 treated with bacteriocins ST69BZ, ST62BZ, ST63BZ, ST611BZ and ST612BZ resulted in leakage of beta-galactosidase from the targeted cells. Two of the five studied bacteriocinogenic strains (ST69BZ and ST612BZ exhibit activity against some fungal cultures). A synergetic effect between bacteriocins ST69BZ, ST62BZ, ST63BZ, ST611BZ and ST612BZ and ciprofloxacin were register.