Quick Study: Research shows how Listeria penetrates small intestine
The fluorescent green flecks are the Listeria monocytogenes bacteria as they invade through the tips of the villi in the intestinal lining, which are outlined in red. The blue stain illuminates the nuclei of the villi.
THE QUESTION: Listeria monocytogenes is a bacterium that can cause potentially fatal infections in the blood (sepsis) or brain (meningitis), or miscarriages in pregnant women.
Raw or contaminated food is the most common way for people to be infected—soft cheeses, deli meats and raw and smoked fish are the usual culprits. Once someone consumes such food, the bacteria that survive the acidity of the stomach may enter the small intestine, crossing the epithelial barrier and then spreading to the liver, spleen, central nervous system and, in pregnant women, the fetus.
The ongoing mystery has been how do the Listeria bacteria get past the epithelial barrier?
THIS STUDY investigated how and where Listeria breaches the tight junctions between the surface cells of the small intestine to invade the body.
The researchers used fluorescently labeled probes to document the various interactions between the bacteria and the intestinal cells. They found that the microbe can invade cells only at the sites where the epithelium is ejecting dead cells—a constant process in this layer of the intestine.
What happens is this: The living epithelial cells briefly loosen their connection with neighboring cells so they can cast out dead ones. This transient breach of the epithelial barrier exposes a protein that Listeria latches onto, hitching a ride to the other side. This is the first time that such a mechanism has been visualized.
WHO MAY BE AFFECTED: According to the Centers for Disease Control and Prevention, about 2,500 cases of Listeriosis are reported in the United States annually, with about 500 deaths.
WHY IT MATTERS: The ability of Listeria to cause severe, invasive disease depends on its ability to cross the intestinal epithelium. By learning more about how it does this, researchers may devise better ways to protect against Listeria.
Currently, the only preventive measures are thorough cooking and cleaning of food and pasteurization of dairy products. Antibiotics are the primary treatment for Listeriosis.
CAVEATS: The researchers explored how Listeria gets through the outer layer of the small intestine in cells in culture and in a susceptible animal model, the rabbit, but their work needs to be confirmed in humans. It also did not address how the bacteria travel from the intestine to cause deeper infection.
STANFORD CONNECTION: All of the authors were at Stanford when the work was done. Both senior authors—associate professor Julie Theriot, PhD, and assistant professor Manuel Amieva, MD, PhD—are in the Department of Microbiology and Immunology. Theriot is also in the Department of Biochemistry. Amieva is also in the Department of Pediatrics.
The first author, Mickey Pentecost, is a graduate student in Amieva's lab. Glen Otto, DVM, the fourth author, was associate professor of comparative medicine.
FIND THIS STUDY: Published in the Jan. 26 online issue of Public Library of Science-Pathogens: http://pathogens.plosjournals.org. A photograph from the study is featured on the cover of the journal's January print issue. —Mitzi Baker
