Evidence for the existence of microbiota in the placenta and blood of pregnant mice exposed to various bacteria

Whether or not bacteria exist in the placenta is a controversial issue. In the present study, bacteria in the placenta and blood of pregnant mice were evaluated after administration of Enterococcus faecalis, Lactobacillus reuteri, Lactococcus lactis, Lactobacillus johnsonii, Streptococcus thoraltensis, and Staphylococcus epidermidis. Results showed that 57.14–85.71 ​% of the placentas and 71.43%–100 ​% of the blood samples positively existed spherical and/or rod-shaped bacteria. All collected placentas treated with or without propidium monoazide were shown to harbor various bacteria using the denaturing gradient gel electrophoresis (DGGE) method. Moreover, E. faecalis and L. lactis were characterized as the dominant and common bacteria in each group. Our results prove the existence of bacteria in the placenta and blood of pregnant mice, which provides clues for researchers to study the role of these bacteria on host health and the development of the fetus.