Resumo

Colibacillosis is one of the main causes of neonatal diarrhea in calves and can compromise the calf’s digestive tract. The administration of probiotics represents a promising alternative to the treatment with anti-bacterial medication. The objective in this research was to quantify characterize and select strains of lactic bacteria with probiotic potential from Nellore calves in Northern Minas Gerais. Fecal samples were collected from six healthy suckling subjects, aged three to ten days and from those same animals at three months. The samples were diluted and inoculated in plates containing MRS medium in anaerobic chamber at 37°C for 48 hours. After this period, colony quantification was performed and was selected different morphotypes shown in culture. After reisolation and quantification, to twenty six Lactobacillus spp. isolates, biochemical characterization was performed using API 50 CH test, resistance to acid pH and bile salts and in vitro antagonistic ability to two Escherichia coli strains from calves with colibacillosis and to an ATTC E. coli strain. Significantly higher population of lactic bacteria was verified for the calves’ feces at colostral phase (p<0.001 in Student's t-test).At three months of age, the calves were already consuming other foods like tips of grass and mineral salt, which would favor other microorganisms that could compete with the lactic acid bacteria. Regarding resistance to hydrochloric acid, 92.3% of neonatal calf’s isolates resisted to pH 4.0 that was and a significantly higher rate than three-month-old calf’s isolates. In the maximum bile salts concentration of 1%, 92.3 and 84.6% of new-born and three-month-old calves isolates respectively, resisted and presented growth. On the test for antagonism to Escherichia coli strains, the isolates Be4 1m, Be1 2b and Be6 2a respectively identified as Lactobacillus salivarius, L. crispatus and L. pentosus produced inhibition halo. Specifically, the L. salivarius isolate presented an inhibition halo with 20mm of diameter against the E. coli strain from the small intestine of a two-month calf with diarrhea. These Lactobacillus spp. isolates presented better resistance to acid pH and bile salts, indicating potential for being rated as probiotics