Crude extracts of metabolites from co-cultures of lactic acid bacteria are highly antagonists of Listeria monocytogenes

Listeria monocytogenes is a pathogen difficult to control, due to its resistance to extreme conditions. The antimicrobial activity of a mixture of metabolites produced by lactic acid bacteria was evaluated against L. monocytogenes. Bacterial combined cultures in 1:1 ratio of Lactobacillus plantarum and Weissella cibaria (treatment LP + WC) and mixtures in ratio 1:1:1 of Lactobacillus brevis, L. plantarum, and W. cibaria, (treatment (LB + LP + WC) were grown by discontinuous fermentation, at 32 degrees C for 48 h. At 1, 2, 6, 12, 24 and 48 h of fermentation, samples were taken, the biomass was separated from the metabolites, and the antimicrobial activity of the metabolites was measured in vitro against L. monocytogenes. For comparison, experimental data published in the literature corresponding to monocultures of L. brevis (L.B), L. plantarum (LP) and W. cibaria (WC) were used. The antimicrobial activity was measured by a surface diffusion technique using absorbent paper discs impregnated with 60 mu l from each metabolite and placed on the TSA agar surface (36 degrees C, 24 h). The metabolites from the microbial mixtures showed statistical differences with respect to their respective monocultures. With the treatment (LP + WC) an inhibition diameter of 2.54 cm was obtained at 12 h of fermentation, this value was higher than those obtained in the monoculture LP (2.19 cm), and WC (2.44 cm), during the same period. In the mixture (LB + LP + WC) during the first 12 h of fermentation, the antimicrobial activity was higher (2.12-2.28 cm) than the antimicrobial activity of the monoculture LB (1.66-2.23 cm). The use of metabolites from the co-culture of L brevis, L. plantarum and W. cibaria under the evaluated conditions, potentiate the antimicrobial activity of L. brevis against L. monocytogenes, therefore, they are promising in bio-preservation.