Bacteria Assails Immune System with Toxin

A Streptococcus bacterium invades the placenta with the aid of a neutrophil-puncturing pigment.

Oct 18, 2016
Ben Andrew Henry


Group B Streptococcus, a bacteria linked to preterm birth and newborn infections, deploys a toxic pigment molecule that targets immune cells in order to infect the placenta and amniotic sac, according to new research.


In a study published this month (October 14) in Science Immunology, University of Washington researchers observed pregnant macaques infected with strains of GBS, some with strains that could produce the pigment and some with strains that could not, finding an association between presence of the pigment and problems during birth.


The role of this toxic pigment, the researchers found, is to puncture the membrane of neutrophils, immune cells that trap pathogens in sticky expulsions of DNA and chromatin. The pigment “doesn’t make a nice defined hole,” study coauthor Lakshmi Rajagopal told Science News. “It inserts in random places, disfiguring the membrane.”


Neutrophils are the placenta’s first and principal line of defense, study coauthor Kristina Adams Waldorf told Science News. “If a placenta can’t rely on its neutrophils to get rid of infection, it’s really in trouble.” Neutrophils have also been found to lead T cells to an infection site in influenza cases.


Group B Strep infection is relatively common in people and doesn’t always trigger problems during birth. Predicting whether an infection will be dangerous or harmless remains a challenge, Maria Gloria Dominguez-Bello of New York University told Science News: “Why can we live with such a potential enemy? And how can we avoid the virulent strains?”


Determining how this bacterium operates could aid in vaccine development, Rajagopal told Science News. But studying the pigment is challenging, because it’s made of a fatty chain that’s not soluble in water. “First we have to make enough that we can tinker with it,” she added. “It’s tricky.”