**4.6 Modulation of the intestinal microbiota**

Studies have shown that some probiotics can be used to treat intestinal diseases [106, 107] because they have the ability to improve the oxidative stress created by changing the composition of the microbiota. In fact, probiotics show their antioxidant properties by settling in the gastrointestinal tract [108, 109] to regulate the altered microbiota composition and prevent the proliferation of harmful bacteria. Based on researches, *Lactobacillus* and *Bifidobacterium* are among the probiotics that prevent the growth of pathogenic bacteria by lowering the pH of the intestine; as a result, a balance is established in the composition of the microbiota [110, 111]. In addition, some probiotics produce toxic compounds (such as organic acids, bactericides, and biosurfactants) against pathogenic microorganisms [112]. For example, *Lactobacillus rhamnosus* GG, suppresses different bacteria by producing antimicrobial compounds [113]. As previously mentioned, the use of probiotics leads to improving oxidative stress by modulating the composition of gut microbiota and reducing the abundance of harmful bacteria.
