Aim To evaluate two folate-producing strains, Streptococcus (Strep.) thermophilus CRL 808 and Strep. thermophilus CRL 415, against chemically induced mucositis in mice. Methods and ResultsConclusionIn vitro assays with Caco-2 cells were performed to evaluate the effect of the bacteria in the presence of 5-fluorouracil (5-FU). For invivo studies, mice were daily injected with 5-FU to induce intestinal mucositis (IM) and orally administered with folate-producing strains during 6days. Clinical symptoms, histological parameters and cytokine profiles were assessed. The results showed that Strep. thermophilus CRL 808 increased the cytotoxicity of 5-FU against Caco-2 cells. Administration of this strain in mice with chemically induced IM resulted in a reduction in diarrhoea score and restoration of the intestinal architecture. Cytokine analysis showed that the anti-inflammatory effect by the bacterium is not associated with an immune mechanism. Regarding Strep. thermophilus CRL 415, no improvements were observed in any of the parameters evaluated. The administration of the folate-producing Strep. thermophilus CRL 808 has the potential to prevent IM induced by 5-FU in mice. Significance and Impact of the StudyFolate-producing LAB could be used in chemotherapy patients to reduce the symptoms of IM, improve their nutritional status and increase the effectiveness of 5-FU.