SELECTION OF Lactobacillus STRAINS ISOLATED FROM Rana catesbeiana HATCHERIES FOR THE PRODUCTION OF INHIBITORY METABOLITES

PASTERIS, S.E.; ROIG BABOT, G.; MONTEL MENDOZA, G.; BUHLER, M.I.; NADER-MACIAS, M.E.

Tucumán-Argentina

Simposio; II INTERNATIONAL SYMPOSIUM ON LACTIC ACID BACTERIA. FIRST ARGENTINEAN LAB NET MEETING; 2006

The application of probiotic products in aquaculture has acquired a high interest in the last years, mainly the use of Enterococcus faecium and Lactobacillus spp strains. Rana catesbeiana is considered a fishery product and the presence of some diseases in hatcheries, such as red-leg syndrome (RLS) can produce animal mass mortality with high economical losses. In previous works, we demonstrated that Lactobacillus strains grown in LAPTg medium showed a low inhibitory effect on RLS-associated pathogens what could be attributed to organic acids. In this work, we studied the inhibitory activity of Lactobacillus strains against RLS-related pathogens and food spoilage bacteria by growing in other culture media (MRS). Lactobacillus strains were isolated from different places of the hatchery during June and July, and they were grown in MRS broth for 24 h at 37°C. Homologous and heterologous indicator strains were grown in nutritive and BHI broths. The inhibitory effect of neutralized and catalase treated lactobacilli supernatants were measured by the well-diffusion method. The plates were incubated for 24 h at 37°C and the inhibitory activity was expressed as mm of inhibition. The results showed that the strains isolated in June from the skin of healthy animals, non-healthy animals and food presented a low inhibitory level against the assayed pathogens. The inhibitory effect was due to acidity. However, Lactobacillus 9U isolated from food, inhibited RLS-associated pathogens  by both, acidity and H2O2. The strains isolated in december showed a good inhibitory profile against pathogens of R. catesbeiana hatchery and food borne bacteria The effect was due to acidity according with the low pH achieved by the supernatant cultures. Under our experimental conditions, the strains isolated from non-healthy animals presented a low inhibitory activity against Listeria monocytogenes and Salmonella enteritidis, effect that could not be observed in others tested lactobacilli. These results indicate that the antagonic activity of lactobacilli depends on the initial concentration of the indicator strains and the area of the hatchery where they were isolated. The results obtained allow us to select a group of Lactobacillus strains which could be used as probiotic for R. catesbeiana, with special interest in Lactobacillus 9U.