Researchers find that GBS bacteria produce small balloons called membrane vesicles with toxins that kill both foetal and maternal cells.

Indian researchers have made a major discovery by understanding the mechanisms by which preterm births (between 28 and 32 weeks of gestation) occur. At 35 per cent, India accounts for the highest burden of preterm births in the world.

The researchers found for the first time that gram-positive Group B Streptococcus (GBS) bacteria produce small balloons called membrane vesicles, which contain toxins that kill both foetal and maternal cells and destroy the collagen that binds the cells together.

The team was led by Professor Anirban Banerjee from the Department of Biosciences and Bioengineering, IIT Bombay, and Dr. Deepak Modi from Mumbai’s National Institute for Research in Reproductive Health. The results were published on September 1 in the journal PLOS Pathogens.

Group B Streptococcus (GBS) bacteria are normally found in human vagina and their numbers can shoot up in some pregnant women. The GBS bacteria have been associated with premature rupture of amniotic membrane and preterm birth.

“Other closely related bacteria have been known to produce vesicles in very recent times. So we were interested in knowing if Group B Streptococcus bacteria were producing vesicles,” says Prof. Banerjee.

“Besides curiosity, there is a scientific reason too. A lot of women who suffer from inflammation of the amniotic membrane do not have bacterial infection in the amniotic sac. So we thought that the bacteria present in the vagina were secreting certain factors that travels up the reproductive tract and acted in a synchronised fashion to cause preterm birth and stillbirth.”

The team tested its hypothesis by injecting vesicles into 15 pregnant mice. All the injected mice gave birth to preterm babies and nearly 40 per cent were born dead (stillborn). The preterm babies were much smaller and unhealthy. In mice, the babies were born two days preterm.

“This is equivalent to two months in humans as the gestation period in mice is 21 days,” says Dr. Modi.

The researchers found that the toxins present in the vesicles fragmented the collagen of the amniotic membrane. “Fragmentation of the collagen leads to loss in elasticity and weakening of the amniotic membrane thus making it susceptible to rupture due to pressure from the growing foetus,” says Dr. Modi. This leads to preterm birth. The vesicles also degrade the collagen in the womb.