The bacterium-bacterium interaction between pathogenic and probiotic Enterococcus as well as the bacterium-host interaction between Enterococcus and intestinal epithelium has drawn increasing attentions, but the influence of those interactions on host pregnancy remains largely unexplored. In the present study, we evaluated the effects of probiotic E. faecalis Symbioflor 1 or/and pathogenic E. faecalis OG1RF on the miscarriage of pregnant mice. Using in vitro assays of competition and exclusion and displacement, antagonistic property of E. faecalis Symbioflor 1 against E. faecalis OG1RF was observed, and the former inhibited the translocation of the later in vivo. The rate of miscarriage induced by E. faecalis OG1RF challenge was significantly reduced by 28% with E. faecalis Symbioflor 1 intervention; and the tissue integrity of ileum, colon, uterus, and placenta and placental blood cell density in pregnant mice were drastically improved by such probiotic intervention. Compared with the controls, probiotic intervention significantly upregulated the level of IL-10 and TGF-β, downregulated levels of IFN-γ, and increased progesterone level that reversed the trend of being Th1 predominance state reported for adverse pregnancy outcome at early pregnancy stage. In conclusion, E. faecalis Symbioflor 1 decreased the translocation of E. faecalis OG1RF, prevented pathogen-induced tissue damage, and changed Th1-Th2 homeostasis toward Th2 predominance during early pregnancy resulting in decreased miscarriage. KEY POINTS: •The mechanism of how probiotic E. faecalis Symbioflor 1 improves pregnancy of mice • Influence of interactions of pathogenic and probiotic Enterococcus on host pregnancy • E. faecalis Symbioflor 1 change Th1-Th2 homeostasis toward Th2 predominance.
Keywords: Antagonistic property; E. faecalis Symbioflor 1; Pathogenic translocation; Pregnancy miscarriage; Th1-Th2 homeostasis.