The treatment of mice with Lactobacillus casei induces protection against Babesia microti infection.

In this study, we report that administration of Lactobacillus casei confers protection to mice against the intracellular protozoan Babesia microti. Mice treated with L. casei orally or intraperitoneally were inoculated 7 days later with an infectious dose of B. microti. Mice treated with lactobacilli showed significant reduction in the percentage of parasitized erythrocytes (PPE) compared to untreated mice. When mice were inoculated intraperitoneally with L. casei 3 or 0 days before challenge with B. microti, the PPE was significantly lower compared to untreated mice and there were no differences between treated mice and mice immune to B. microti infection. When mice treated with live or dead L. casei were compared to mice inoculated with Freund Complete Adjuvant before a B. microti infection, a significant reduction of PPE was observed. These results show the protective effect of L. casei administered to mice against a B. microti infection and suggest that it might act by stimulating the innate immune system.