Application of in vitro methods for selection of bovine origen Lactobacillus salivarius strains as probiotics

SOTO, L.P.; FRIZZO, L.S.; BERTOZZI, E.; ZBRUN, V.; SEQUEIRA, G.J.; ROSMINI M.R.

Rosario, Santa Fe.

Congreso; Congreso Argentino de Microbiología General; 2008

Sociedad Argentina de Microbiología General (SAMIGE)

The rearing of calves in intensive systems that separates them from their mothers at an early age, hindering the colonization of the indigenous intestinal microbiota and facilitates the activity of pathogenic microorganisms causing economic losses. Probiotics have been defined as ?living microorganisms, which upon ingestion in certain numbers, exert health affects beyond inherent basic nutrition?. The inoculation of probiotics during the first days of life of the animal allow intestinal colonization with bacteria that exert a protective role against infections. The selection of probiotics before incorporation in diet requires close scrutiny in the form of in vitro as well as in vivo tests. The present study was undertaken to check different in vitro characteristics of nine Lactobacillus salivarius strains of bovine origen. The characteristics studied include aggregation, coaggregation and inhibition tests with Escherichia coli  and Salmonella dublin DSPV 595T. Lactobacillus were grown in MRS broth, then were centrifugated and the cells were separated from the supernatant. The cells were resuspended in 1 ml of Ringer ¼ solution to which was added 100 µl of the supernatant for the aggregation test. Pathogen strains were grown in BHI broth and once centrifugated, the cells were resuspended in ringer ¼ solution. For the coaggregation study, 450 µl de Lactobacillus suspensions were added with 450 µl of the pathogen suspensions and 100 µl of Lactobacillus supernatant. In both studies, the presence of precipitate was indicating the aggregation or coagregación capacity of the lactobacillus strain. The inhibition was assessed by inoculating of pathogenic microorganism in agar BHI. Before the incubation of the plates, holes were made in the agar and the supernatants were placed in them. The inhibition of bacterial growth was verified by the presence of areas without cell growth around the hole. Six strains resulted positive to the aggregation test, of which five coaggregated with both pathogens and the remaining strain aggregated only with S. dublin. The inhibition test was positive for all strains evaluated when they were confronted with S. dublin, but only five of them inhibited the growth of E. coli. The ability to antagonize these pathogens was attributed to production of organic acids and no specific compound caused the inhibitory effect. Only three strains were able to aggregate, coaggregate and inhibit the growth of both pathogens. This study shows the variations between different strains of L. salivarius, isolated in the same ecosystem, on some probiotic properties and that is why it is advisable the screening of the best microbial exponents for the development of a probiotic inoculum.