1. A composition for use as a medicine containing a mixture comprising at least one bacterial strain belonging to a species selected from the group consisting of Bifidobacterium lactis, Lactobacillus acidophilus and Lactobacillus brevis, and having antioxidant properties. The composition according to claim 1, wherein said at least one bacterial strain having antioxidant activity is selected from: Bifidobacterium lactis BS 05 (ID 1666) deposited Probiotical SpA, Novara (Italy) in the German collection of microorganisms and cell cultures (DSMZ) in Germany on October 13, 2009 and having a deposit number DSM 23032, - Lactobacillus acidophilus LA 06 (ID 1683), deposited by Probiotical SpA, Novara (Italy) in DSMZ in Germany on October 13, 2009 and having a deposit number DSM 23033, and - Lactobacillus brevis LBR01 ( ID 1685), deposited by Probiotical SpA, Novara (Italy) at DSMZ in Germany on 10/13/2009 and having deposit number DSM 23034.3. The composition according to claim 1 or 2 for use in the treatment of pathologies or dysfunctions associated with oxidative stress, preferably in cases in which oxidative stress has been caused by medication. A food composition or additive containing a mixture comprising at least one bacterial strain belonging to a species selected from the group consisting of Bifidobacterium lactis, Lactobacillus acidophilus and Lactobacillus brevis, and having antioxidant properties, preferably said at least one bacterial strain having antioxidant properties selected in accordance with clause 2.5. The composition according to claim 1 or 4, wherein said composition contains bacteria in a concentration of from 1 × 10 to 1 × 10 colony forming units (CFU) / g of mixture, preferably from 1 × 10 to 1 × 10 CFU / g of mixture, even more preferably comprising1. Композиция для использования в качестве лекарственного средства, содержащая смесь, включающую по меньшей мере один бактериальный штамм, принадлежащий к виду, выбранному из группы, содержащей Bifidobact
