Bacterial infection to blame for premature deliveries, stillbirths

A new study has linked premature deliveries and stillbirths to a bacterial infection found in a pregnant woman’s vagina or rectum.

According to the study, carried out jointly by Bhabha Atomic Research Centre (BARC), National Institute for Research in Reproductive Health (NIRRH), and Indian Institute of Technology Bombay, a class of bacteria called Group B Streptococcus (GBS), found in 20 to 20 percent of all women, produces membrane-bound vesicles which move from the vagina to the uterus and cause inflammation of the membranes surrounding the foetus, leading to premature and stillbirths. The study has been published in PLoS Pathogens on September 1, 2016, a press release issued by IIT Bombay stated.

Every year, 15 million babies are born preterm — more than 1 in every 10 babies — and almost a million children die each year due to resulting complications. Premature delivery is the single largest cause of death among infants and young children; and survivors face a lifetime of disability, including neurological problems, learning disabilities, visual and hearing problems.

GBS is regularly tested for in late pregnancy. To establish its link to premature deliveries wasn’t easy: not only are most women asymptomatic but also many with GBS deliver preterm but the infection is rarely found in the womb.

Researchers Prof. Anirban Banerjee, microbiologist with IIT Bombay, and Dr. Deepak Modi, Reproductive Biologist with NIRRH, studied if GBS made small micro-particles (membrane-bound vesicles, or MVs), which would then move up in to the womb and cause tissue damage. Since GBS is not known to produce such MVs, the team started growing GBS in liquid media. When they removed the bacteria and examined the remaining liquid by electron microscopy, they found numerous small spherical structures. Zooming in on the surface of growing bacteria revealed vesicles budding off the bacterial cell, confirming that GBS produces MVs.

“This was a breakthrough in my lab as these vesicles were found to be loaded with tons of bacterial virulence factors, particularly toxins and collagen degrading proteases,” said Prof. Banerjee. The researchers then deposited the MVs without the bacteria into the vagina of mice and, hours later, found them throughout the uterus and in the developing foetus.

Prof. Banerjee said that the MVs could also lower the elasticity of the membrane holding the foetus, so that it can’t expand to accommodate the growing foetus, leading to its rupture and preterm birth. The researchers then injected the MVs into the amniotic sac of pregnant mice and found that all the mice exposed to the MVs gave birth prematurely and the babies born were much smaller and unhealthy. Dr. Modi said the symptoms the GBS MVs caused in micewere similar to those found in women with a GBS infection.

Acknowledging that these were experimental results in mice, Prof. Banerjee and Dr. Modi said that the discovery is a paradigm shift, as it shows GBS, by simply sitting in the vagina, can damage the baby in the womb without physically going there, and cause preterm birth. Prof. Banerjee said, “As the vesicles are not sensitive to antibiotics, treatment with antibiotics will not help to prevent preterms caused due to these MVs”.The researchers said this will pave the way for discovery of new drugs to halt the vesicle production by GBS.