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."

The study will be posted on June 30 in the June issue of the online journal PLoS Pathogens.

Listeriosis is a foodborne illness caused by Listeria monocytogenes. Every year in the United States, about 2,500 people fall seriously ill with the disease. About one in three cases occur in pregnant women, and about one in five of all cases results in death, according to the Centers for Disease Control and Prevention (CDC). Apart from pregnant women, the illness primarily affects infants and people with compromised immune systems.

Fever, muscle aches and sometimes gastrointestinal problems are among listeriosis's most common symptoms. In pregnant women, however, the symptoms are often mild, yet the illness freq
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Contact: Liese Greensfelder
510-643-7741
University of California - Berkeley
3-Jul-2006