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The placenta is not as sterile as once thought. New research shows that the placenta harbors a unique, low abundant microbiome, said researchers from Baylor College of Medicine and Texas Children’s Hospital.

The findings, in the current issue of the journal Science Translational Medicine, provide important new insights on the structure of the placental microbial community, the organisms present, and how they might be capable of impacting a pregnancy.

“After we completed our studies of the vaginal microbiome in pregnancy, we noted that the most abundant microbes in the mom’s vagina were not what populated the baby’s intestinal microbiome,” said Dr. Kjersti Aagaard, associate professor of obstetrics and gynecology in the section of maternal fetal medicine at Baylor and the Texas Children’s Pavilion for Women, and the lead and corresponding author on the report. “We reasoned that there must be another source ‘seeding’ the infant’s gut at birth, so we sought to examine the placenta.”

The microbiome is the population of microbes – bacteria, viruses and fungi – that cohabit with human cells and help cells complete their tasks. Understanding what characterizes the microbiome communities is essential for understanding human development, Aagaard said.

Aagaard and her colleagues are key members in the collaborative National Institutes of Health funded Human Microbiome Project, which seeks to further characterize these communities and how they relate to health and healing human disease.

In this study, the first and largest study to focus on the placental microbiome, 320 human subjects’ samples were analyzed comprehensively following a process called shotgun metagenomic sequencing. This technology enables microbiologists to uniquely evaluate bacterial diversity and detect the abundance of specific microbes and all their genetic pathways in a community.