Each year an estimated 15 million babies are born preterm; complications from the condition are the leading cause of death among children under 5 years of age. A new study may have found an underlying cause of preterm births, a discovery that could someday save millions of young babies' lives each year.

B streptococcus (GBS), a group of bacteria found in the vagina and rectum of 20 to 30 percent of women, may increase the risk of preterm birth. According to the study, GBS produces membrane-bound vesicles (MVs) containing bacterial factors that can attack host tissue. In mice, these vesicles can move from the vagina to the uterus and cause inflammation of the membranes surrounding the fetus. When injected directly into the amniotic cavity of mice, these MVs can induce preterm and stillbirths.

In most cases, GBS cause no problem, but the MVs they produce are loaded with toxins, which can cause tissue damage. The researchers hypothesized that in pregnant women who carry GBS and deliver prematurely, the bacterial infection might move up to the womb during pregnancy and cause tissue damage at the interface between mother and fetus.

To test this theory, the team deposited MVs without GBS bacteria into mouse vaginas and hours later found them throughout the uterus and in the developing fetus. This showed that MVs do have the ability to travel up the birth canal. When the researchers injected MVs directly into the amniotic sac (the fluid-filled cavity surrounding the embryo) of pregnant mice, they observed that 24 hours later the tissue of the interface between mother and fetus was severely disrupted, with broken collagen fibers, hallmarks of inflammation, and signs of extensive cell death. In addition, Approximately 60 percent of the fetuses were born prematurely compared with only 10 percent of pups following control injection with saline.

The research has not yet been repeated in humans so its not clear if the bacteria causes the same preterm risk in pregnant women. However, if the same proves true for humans, the finding could lead to the development of new drugs that would target this bacteria and thus reduce the risk for preterm birth in these women.

Source: Surve MV, Anil A, Kamath KG, et al. Membrane Vesicles of Group B Streptococcus Disrupt Feto-Maternal Barrier Leading to Preterm Birth. PLOS Pathogens. 2016

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