The Listeria bacterium, found in soil and water, can be transmitted to humans via undercooked and unpasteurized food, causing flu-like symptoms or gastrointestinal distress. For individuals with weakened immune systems, listeriosis can be fatal, and infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or infection of the newborn.
The research was conducted by Pascale Cossart, a Howard Hughes Medical Institute international research scholar, and her colleague Esteban Veiga at the Institut Pasteur in Paris, and will be published in the August 21, 2005, issue of Nature Cell Biology. Cossart and Veiga detailed how Listeria invades cells by activating cellular machinery that transports viruses, small molecules, and proteins. Once it has safely entered a cell, the microbe can replicate and continue the process of infection.
The body usually deals with bacteria and other large, foreign microbes through a process called phagocytosis. Specialized cells engulf the invading microbe and destroy it. Scientists long believed that cells use a second process, called endocytosis, to deal with smaller molecules or viruses. In endocytsosis, a cell's outer membrane pinches inward around the target to form a pocket that's brought inside the cell, creating a structure called a vesicle.
"Phagocytosis and endocytosis may, in fact, be more similar than past research suggests. This is a totally new concept," Cossart says.
Cossart's lab had observed that Listeria ?which is 20 times the size of the largest particle scientists believed a cell could take in by endocytosis ?could invade non-phagocytic cells. Other labs
Source:NIH/National Institute on Aging