Evaluation of protective effect of probiotic in sheep against experimental infection by Escherichia coli

Domestic ruminants, especially sheep and cattle, are the main reservoirs of Shiga toxin-producing Escherichia coli (STEC) and may transmit this pathogen to human. Probiotics are "live organisms that, when administered in adequate amounts, confer a health benefit on the host", decreasing the infection and its dissemination. However, these benefits are conferred only after the colonization of probiotic strains in the gut of the animal, which may be impaired by normal microbiota. The aims of this study were to determine whether the inoculation of sheep with probiotic strains decreases the shedding of STEC and to determine whether the age of sheep interferes with this protective effect. Sheep that received oral inoculums at a concentration of 2 × 109 cells per mL of viable STEC bacteria, which are carriers of stx1, stx2 and eae genes, were compared with other sheep that did not receive inoculums. When probiotic bacteria were inoculated together with the STEC, the number of pathogenic bacteria in the population was similar to the control. The protective effect of probiotic strains was largest in groups with younger animals than with older animals. These findings suggest that the use of probiotic strains in sheep may decrease the intestinal shedding by STEC as well as the fact that the age of the sheep may interfere in the protective effect of probiotics against colonization by STEC.   Key words: Probiotic, protective effect, Escherichia coli, sheep.