For years, doctors have puzzled over why pregnant women are 20 times more likely than others to be infected by the bacterium Listeria monocytogenes. Researchers at the University of California, Berkeley, now think they have the answer, and it isn’t pretty.
Their research, conducted in guinea pigs, shows that the bacteria can invade the placenta, where – protected from the body’s immune system – they proliferate rapidly before pouring out to infect organs such as the liver and spleen. The illness they cause often results in miscarriage or infection of the fetus.
The study is the first to trace such a pathway of infection, and it dashes the widely-held assumption that immune-system changes during pregnancy are to blame for elevated Listeria infection rates.
“The reason the mother is more susceptible is not necessarily because her immune system is compromised, but because the bacteria that got into her placenta are infecting her,” said Anna Bakardjiev, the study’s lead author and a postdoctoral researcher with Daniel Portnoy, professor of biochemistry and molecular biology at UC Berkeley. “The miscarriages that result from these infections may be a natural defense mechanism to dispel this source of infection.”
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