Researchers have found that small communities of bacteria exist in one of the least likely sites for the presence of bacteria: the placenta. The placenta is the organ that provides nutrition to the fetus through the umbilical cord. This finding overturns the traditional understanding that the placenta is sterile. The study also showed that: these bacteria may come from the mouth, confirming that good oral hygiene may be important for a healthy pregnancy. The placenta is a pancake-like piece of tissue located on the side of the uterus that provides oxygen and food to the fetus and also has the role of removing metabolic waste from the fetus. For a long time, medical experts believed that any bacteria found on the placenta must have been contracted after delivery when the placenta passed through the vagina. Recently, however, researchers have realized that babies contain a community of bacteria in their intestines as soon as they are born. The bacteria in the fetal intestine do not match those in the vagina, suggesting that there are other sources of these bacteria, such as the placenta, according to fetal medicine expert Lu Gao of Baylor College of Medicine in Houston, Texas. Agarde and colleagues are co-investigators with the Human Microbiome Project in the United States. “The Human Microbiome Project is working to study the microbiomes – the bacterial, fungal and viral communities – that live in all parts of our bodies. Researchers collected placental tissue from 320 pregnant women and analyzed the tissue for microbiomes on the placenta. To determine the types and numbers of microbes and the genes they carry, the researchers extracted DNA from these placental tissues and sequenced it, looking for gene fragments and entire bacterial genomes. The analysis showed that the placenta holds a small, diverse group of bacteria, most of which are non-pathogenic strains of E. coli, the main strain in our intestines, in addition to other bacteria belonging to five major phyla. The vast majority are known to be benign bacteria capable of helping, for example, to metabolize vitamins. Surprisingly, this combination of bacteria in the placenta looks more like the microbiome found in an adult’s mouth than the microbiome found in the vagina, skin, intestines or other parts of the body, Agarde’s research team reports today in the journal Science Translational Medicine. The researchers suggest that these bacteria may reach the placenta from the mother’s mouth through the bloodstream, perhaps driving them into the bloodstream when the pregnant woman brushes her teeth. This possibility is very interesting because it is well known that gum disease and preterm birth are interrelated. Indeed, it is true that for women who give birth prematurely – before 37 weeks – the series of bacteria in their placenta is different. ”This study re-emphasizes the importance of oral hygiene during pregnancy,” Agarde said. In fact, she added, perhaps women need to pay attention to dental hygiene before they become pregnant because the placenta develops early in pregnancy; this can be a challenge for low-income women who can’t afford dental care. The team also found that the composition of the placental microbiome and urinary tract infections are interrelated, suggesting that urinary tract infections and the antibiotics used to treat them may alter the microbiome in the placenta in unhealthy ways. Roberto Romero, a perinatal researcher at the National Institute of Child Health and Human Development in Detroit, Mich. Romero said, “The study shows for the first time that all placentas contain small amounts of bacteria.” Washington University in St. Louis biologist Indira Mysoka said, “The study is the first to show that all placentas contain small amounts of bacteria. Mysoka went on to say, “These bacteria may live there for specific purposes, such as seeding the fetus with the gut microbiome or building the immune system for the fetus.” Mysoka has previously reported findings that certain placental cells contain bacteria. However, Romero and other researchers warn that it is too early to say exactly how the placental microbiome gets there and what they are actually doing. It’s also possible that these bacteria were present in the uterus before pregnancy and evolved to resemble oral bacteria, Myosoka said. Microbiologist Seth Bowdenstein of Vanderbilt University in Nashville, Tenn. Despite these unknowns, the discovery of the placental microbiome further illustrates the point that no tissue in the body is sterile, says Bowdenstein.