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Mysterious Bacterial Toxin Linked To Stillbirths


Robin Andrews

Science & Policy Writer

Strep B surrounded by toxic bubbles. Surve et al./PLOS Pathogens

Stillbirth, a baby born dead after 24 to 28 weeks of pregnancy have passed, is a traumatic experience for all involved. Around half of them are linked to complications with the placenta, the organ in the uterus of the mother that nourishes and maintains the fetus. Just last year, there were 2.6 million stillbirths around the world, most of which occurred in low to middle-income nations.

Although the science behind them is slowly becoming clear, there’s much that medical professionals are still yet to learn. Writing in the journal PLOS Pathogens, scientists have found a mechanism through which stillbirths occur in pregnant mice, and the same issue may occur in humans.


Group B Streptococcus, also known as Strep B, is a bacterium that lives in around 30 percent of pregnant women worldwide, often without causing any problems in the lower genital tract. However, in pregnant mice, it appears to produce protein-filled balloons called extracellular membrane vesicles (MVs) that migrate up into the uterus. Once there, they react with the surrounding tissue to cause it to inflame, which can weaken the amniotic sac. If enough damage is done, this could cause a stillbirth to occur.

“In animal studies, we found that the MVs disrupt the connective tissue of the fetal membrane reducing its mechanical strength which may cause premature rupture of amniotic sac,” the authors, led by Manalee Surve of the Indian Institute of Technology-Bombay in Mumbai, write in their study. “Further we show that even in absence of the bacteria, the MVs directly led to extensive inflammation in the mouse resulting in chorio-amnionitis, preterm births and still births.”

These MVs were first spotted using a high-powered scanning electron microscope (SEM). They were analyzed and found to contain corrosive proteins that trigger cell death. Disturbingly, almost all the pups of pregnant mice with these MVs within their amniotic sacs perished either within their expectant mothers (in utero) or were born prematurely.

At this point, it’s unclear why these toxic MVs are manufactured in the first place, but they may be used in turf wars against other bacteria. A similar mechanism was found within human noses just recently, with one type of bacteria producing an antibiotic to kill another, one which happens to be very closely related to the MRSA “superbug.”


Either way, these findings show that a vaccine against Strep B should be a key priority. As reported by Science News, doctors test pregnant women for it between 35 and 37 weeks, and any Strep-positive patients take antibiotics during labor to prevent the infection from spreading to newborns. However, this study hints that an earlier test may be required in order to ultimately prevent possible stillbirths.


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  • pregnancy,

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  • toxin,

  • stillbirth,

  • premature birth