Priešmikrobinius peptidus išskiriančių pienarūgščių bakterijų paieška ir jų genetinė analizė / ; The research of lactic acid bacteria producing antimicrobial peptides and their genetic analysis.

During the fermentation process, lactic acid bacteria produce variety of anti-microbial agents, such as organic acid, carbon dioxide, ethanol, hydrogen peroxide, diacetyl as well as bacteriocins. They contribute to extend the expiration date of foods by using above mentioned anti-microbial agents as natural bio-preservatives. Moreover, bacteriocins are also a great alternative to common antibiotics to which bacteria gain resistance. The aim of this work was to select lactic acid bacteria strains as potential producers of bacteriocins. Firstly, antimicrobial effect of 23 LAB isolates, 15 of which were taken from the collection and 8 were isolated from foods, was evaluated by the agar well diffusion method. This method was applied to sensitive strains of Staphylococcus epidermidis (ATCC 12228) and Pseudomonas aeruginosa (ATCC 27853). From 23 isolates, only 8 most active ones were selected due to their antimicrobial activity of the produced substances remained after neutralization of acids (pH 7) and their antimicrobial activity losts after the use of proteolytic enzyme. Also, by using PCR and sequencing methods, it was confirmed that those 8 isolates have bacteriocin-encoding genes in their genomes. Moreover, the activity of antimicrobial substances remained from -20 to 100 oC. Lastly, phylogenetic analysis showed that 6 out of 8 lactic acid bacteria isolates are related to Lactobacillus sp., 1 is related to Leuconostoc sp. and 1 is related to Lactococcus sp.