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Light shines on action behind foodborne disease Listeria

21-Apr-2004

Delving into the mechanism behind the potentially fatal foodborne disease Listeria monocytogenes (L. monocytogenes), French scientists report their findings this week on how two mammalian proteins are 'hijacked' by the disease.

Foodborne diseases are a widespread and growing public health problem, both in developed and developing countries. In industrialised countries, the World Health Organisation (WTO) estimates that in the US alone around 76 million cases of foodborne diseases, resulting in 325,000 hospitalisations and 5,000 deaths, are estimated to occur each year.

Comprehension of how Listeria monocytogenes invades mammalian cells during infection is vital to understand how this foodborne disease can change from inducing gastroenteritis to serious complications like meningitis, septicaemia, abortion and even death, reports Catarina Amorim.

Scientists from the Institut Pasteur in Paris describe how two mammalian proteins, myosin VIIa and vezatin, are hijacked by L. monocytogenes and used in the propagation of the infection within the host.

"This is a particularly important discovery because in listeriosis, it is the spreading of the infection from the digestive system (the bacteria's entrance door) to the rest of the body that leads to the more serious or even life-threatening complications of the disease," say the researchers.

It is the bacteria's capacity to cross, initially the intestinal wall and later the brain barrier and/or the placenta, three body barriers normally capable of withholding the invasion of infectious agents, that allows the spread of listeriosis and makes it such a big threat to the host.

Sandra Sousa and colleagues at the Unité des Interactions Bactéries-Cellules and the Unité de Génétique des Déficits Sensoriels at the Institut Pasteur report on two proteins of the infected host - myosin VIIa and vezatin - which might explain how L. monocytogenes 'pushes' itself into the host cells.

They describe how disruption in the function of any of these two host proteins leads to an immediate reduction in the number of infected cells, indicating that myosin VIIa and vezatin are crucial for Listeria's cell invasion. The team of scientists also report that both these proteins are recruited to the site of the bacteria's entrance during its internalisation.

Sousa, Cossart and colleagues propose that the mechanism of Listeria internalisation depends on highjacking the host's myosin VIIa and vezatin and using them to create the force that "pushes" the bacteria into the cells. They also found high levels of myosin VIIa in enterocytes, a cell type crucial for the passage of Listeria across the intestinal barrier. This has led the team to propose that the bacteria's capacity of crossing that first body barrier, the crucial step into a widespread, and consequently much more complicated type of infection, is also dependent on the pair myosin VIIa/vezatin.

The global incidence of foodborne disease is difficult to estimate, but it has been reported that in 2000 alone 2.1 million people died from diarrhoeal diseases. A great proportion of these cases can be attributed to contamination of food and drinking water.

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