Bactericidal principle of the fermented aqueous extract of Stevia rebaudiana Bertoni and a possible use of the Stevia extract as a feed supplement for prevention of the digestive tract infections

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We have previously shown that a fermenteds extract from the Paraguayan composite plant, Stevia rebaudiana Bertoni has strong bactericidal activity towards a wide range of food-borne pathogenic bacteria, but it shows no significant killing activity to Bifidobacteria and Lactobacilli. Here we studied bactericidal principle of the fermented extract, and tested the extract for possible use as a feed supplement for prevention of the intestinal tract infections of domestic animals.1. Fermented aqueous extract of Stevia rebaudiana Bertoni was fractionated by the partition with ethyl acetate, followed by the high performance column chromatography using an ODS (CィイD218ィエD2) column. Two bactericidal fractions and one enhancer fraction were obtained. Viability of E. coli was reduced from 10ィイD19ィエD1 cfu/ml to <10ィイD13ィエD1 cfu/ml when incubated with the bactericidal fractions at 37℃ for 1h. One bactericidal fraction has he maximal absorption at 280 nm, and it was sensitive to light irradiation. The other bactericidal fraction was identified as lactic acid.2. In the laboratory experiments, oral administration of the Stevia extract to the Listeria-infected mice decreased the numbers of viable bacteria in the intestinal tract from 10ィイD17ィエD1 cfu/ml to 10ィイD13ィエD1 cfu/ml within 3 days. Oral administration of the extract to the Salmonella-infected calves reduced viable bacteria in the intestinal tract and bacterial tissue invasion.3. In the field experiments, oral administration of the Stevia extract was effective to the intestinal tract infections of piggys. Many of the animals with early-staged diarrhea were recovered within 3 days after the treatment, and their growth rate was normal. Oral administration of the diluted Stevia extract promoted growth of pigs, and the quality of the pork meat was evaluated high at the slaughter house.