ENHANCED ANTIMICROBIAL ACTIVITY OF TWO Lactic Acid Bacteria STRAINS BY CHANGING CULTURE MEDIUM COMPOSITION

GIORDANO A; STAGNITTA P; CASTRO J; BONOMI M; REZZA I

San Luis

Congreso; XXVII Reunión Científica Anual de la Sociedad de Biología de Cuyo; 2009

Sociedad de biología de cuyo

The use of Lactic Acid Bacteria (LAB) in food preservation requires strains with a high degree of antimicrobial activity against foodborne pathogens It is possible to increase their activity varying growth conditions and/or medium composition. The aim of this study was to stimulate the LAB antimicrobial activity and to determine the peptide nature of inhibitory substances present in culture supernatants. Two LAB strains classified as Lactococcus lactis ssp lactis 2 with API CH50 were used in this study. They were grown in Lactobacillus Broth to de Man, Rogosa, Sharpe medium (MRS broth) added of lactose (20 g/l) in replace of glucose (20 g/l) or with high concentration of K2HPO4, incubated at 30ºC for 24-72 h in microaerophilic conditions. The inhibitory capacity determination was performed using the well diffusion method, with Enterococcus faecalis as the indicator strain. Supernatants treated with trypsin and chymotrypsin were used to determine the peptide nature of the antimicrobial substances. The results showed 8 mm and 8.5 mm inhibition halos when lactose or K2HPO4 were added to culture media respectively. Which were significant high in comparison to the base medium (6-7 mm). Replacement of glucose by lactose and an increased concentration of K2HPO4 stimulated the antimicrobial capacity of the two studied strains. Treatment with proteases confirmed the peptide nature of antimicrobial activity, probably bacteriocins, in the LAB culture supernatants.