Isolation, taxonomic identification and hydrogen peroxide production by Lactobacillys delbrueckii subsp lactis T31, isolated from Mongolian yoghurt:: inhibitory activity on food-borne pathogens fool-borne pathogens

Aims: The aim of this work was to isolate lactic acid bacteria (LAB) strains from Mongolian tarag (a traditionally homemade yoghurt) displaying antimicrobial activities against food-borne pathogens, identify inhibitory substances and study the kinetics of their production. Methods and Results: Inhibitory substance-producing bacterial strains were isolated from tarag. From 300 bacterial clones, 31 were able to inhibit the growth of the indicator strain Lactobacillus bulgaricus 340. One of the most active strains was identified as Lactobacillus delbrueckii subsp. lactis strain T31 by using cluster analysis of amplified fragment length polymorphism (AFLP) DNA fingerprints. The antimicrobial substance was inactivated by catalase, demonstrating the production of hydrogen peroxide (H2O2). Production of H2O2 was studied under aerated and nonaerated culture conditions. The amount of H2O2 in the culture supernatant increased during bacterial growth and reached a maximum (5.12 mmol l(-1)) at the early stationary phase under aerated conditions (agitated cultures). H2O2 was not detected in the culture performed without agitation. In mixed cultures performed in milk with either Lact. delbrueckii subsp. lactis T31 in the presence of Escherichia coli, or Lact.. delbrueckii subsp. lactis T31 in the presence of Listeria innocua under aerated and nonaerated conditions, a significant decrease in pathogen count was observed in aerated cultures. Significance and Impact of the Study: The significant decrease in Listeria viability observed in aerated mixed cultures of Lact. delbrueckii subsp. lactis T31 is mainly because of H2O2 production. Lactobacillus delbrueckii subsp. lactis T31 could be used as a protective culture in food industries or as a probiotic to prevent intestinal and urogenital infections.