Common food-borne bacteria may up early miscarriage risk’

Washington, February 21
Moms-to-be, take note! Listeria, a common food-borne bacterium, may pose a greater risk of miscarriage in the early stages of pregnancy than previously thought, a new study has warned.
Researchers at the University of Wisconsin-Madison in the US studied how pathogens affect foetal development and change the outcome of pregnancy.
“For many years, listeria has been associated with adverse outcomes in pregnancy, but particularly at the end of pregnancy,” said Ted Golos, professor at UW-Madison.
“What was not known with much clarity before this study is that it appears it is a severe risk factor in early pregnancy,” said Golos.
Pregnant women are warned to avoid many of the foods – among them unpasteurised milk and soft cheese, raw sprouts, melon and deli meats not carefully handled – that can harbour listeria, because the bacterium is known to cause miscarriage and stillbirth, and spur premature labour, researchers said.
Those severe outcomes have resulted in a zero-tolerance regulatory policy in the US for listeria in ready-to-eat foods, they said.
However, when it occurs, listeria infection in pregnancy may go unnoticed. The few recognisable symptoms are nearly indistinguishable from the discomfort most newly pregnant women feel.
“It is striking that mom does not get particularly ill from listeria infection, but it has a profound impact on the foetus,” said Golos.
Sophia Kathariou, a professor at North Carolina State University, provided a strain of listeria that caused miscarriage, stillbirth and premature delivery in at least 11 pregnant women in 2000.
Four pregnant rhesus macaques were fed doses of the listeria comparable to what one might encounter in contaminated food.
Bryce Wolfe, a UW-Madison graduate student and lead author of the study, monitored the speed and progression of listeria’s spread.
None of the monkeys showed obvious signs of infection before their pregnancies came to abrupt ends.
However, in tissue samples taken after each monkey experienced intrauterine foetal death, Wolfe found listeria had invaded the placenta – the connection between the mother-to-be and the foetus, which usually prevents transmission of bacteria – as well as the endometrium, the lining of the uterus.
“When you introduce a pathogen into the midst of this, it is not very surprising that it is going to cause some sort of adverse outcome disrupting this balance,” Wolfe said.
The researchers believe the inflammation caused by the maternal immune response to the fast-moving listeria also affects the placenta, keeping it from protecting the foetus.
“It should be a barrier. But we are hypothesising that the maternal immune system’s attempt to clear the bacteria actually results in collateral damage to the placenta that then allows the bacteria to invade the foetus,” Golos added.
The research was published in the journal mBio.