Way to protect babies from Listeria found

By Roger Highfield, Science Editor

Last Updated: 7:01pm BST 17/09/2008


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The death of around two dozen babies each year in the UK could be prevented as a result of the discovery of how a disease-causing bacterium crosses the placenta from mother to unborn child.

Infection with Listeria monocytogenes in healthy adults causes a mild flu like illness however, the infection can result in meningitis or blood poisoning in new born babies.

According to the Health Protection Agency, last year alone there were 28 infected babies of which 23 died, mostly as a result of miscarriage and still birth. The babies that survive often suffer severe damage.

Now, thanks to studies of gerbils and mice, Prof Marc Lecuit and Prof Pascale Cossart of the Pasteur Institute, Paris, and colleagues have discovered how the bacterium manages to move from mother to unborn child.

The infection begins with ingestion of food contaminated with Listeria monocytogenes, which can then cross the intestinal barrier and reach the bloodstream.

The bacterium is then able to cross the barrier between the blood vessels of the brain (blood-brain barrier) or cross the placenta to disseminate to the fetus in pregnant women.

They report in the journal Nature that two bacterial invasion proteins, InlA and InlB, are required for the bacterium to target and cross the placental barrier, marking the first time that this has been revealed.

"It helps understand why some Listeria strains (those that express a functional InlA), but not others (that express a truncated version of InlA) lead to placental infection," says Prof Lecuit.

Understanding how the microbe is able to cross the host's natural barrier, latching on to two specific molecules in the placenta (E Cadherin and Met) could help in the development of inhibitory molecules for use as drugs.

The idea would be that the drugs would prevent the bacterium from latching on to the placenta, explains Prof Lecuit. "It is too early to tell when inhibitory molecules could be tested in patients, and the molecule that would be tested first. The idea would be to use a compound able to inhibit InlA-E Cad and/or InlB-Met interactions."

Widespread in nature (water, soil, plants, animals) the bacterium can contaminate many foods: raw vegetables and ready-to-eat foods, such as prepacked sandwiches, pâté, butter, soft mould-ripened cheeses, cooked sliced meats and smoked salmon.

As well as pregnant women, the elderly and immunocompromised - such as Aids, blood cancer or organ transplant patients - are also at risk.

Among them listeriosis is responsible for septicemia, meningitis and encephalitis. Antibiotics are in most cases effective but the infection is nevertheless still lethal in 20 to 30 per cent of infected individuals. In healthy adults, symptoms are generally less severe and can result in a simple gastroenteritis.



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