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How a common throat bacteria can lead to meningitis

By Michael Evans - 07 Mar 2011 16:6:0 GMT
How a common throat bacteria can lead to meningitis

In the majority of cases, the localised presence of Neisseria meningitidis in the throat is of no particular consequence. However, if this heterotrophic gram-negative diplococcal bacterium should migrate from its favoured location (the throat) it is known that meningitis or septicaemia can be the result.

The seriousness of these two infections has led to worldwide research in an effort to improve understanding of the way this bacterium operates and how it transforms itself from being something that is relatively harmless to something that is extremely dangerous.

A French research team directed by Guillaume Dumenil has recently discovered how this bacterium leaves the throat and enters the bloodstream. The results of their research were published in a recent issue of the journal Science.

The team, known as the Avenir team, are part of the Inserm Mixed Research Unit 970, ''Paris centre de recherche cardiovasulaire'' based at the Universite Paris Descartes. Inserm is the French Institute for Health and Medical Research.

Neisseria meningitidis is a bacterium that is specific to humans. It is frequently present in a harmless state in the throats of between 5% and 30% of the population. Although generally harmless, it can prove dangerous in some cases. The throat is where the bacteria multiply and this is its port of entry from where it can disseminate into the bloodstream.

Having got into the blood stream the way is open for the bacterium to enter the brain. The result is septicaemia or meningitis. Since the mortality rates linked to both of these infections are very high, rapid response is vital.

Guillaume Demenil and his Inserm team were anxious to find out more. "Certain advances made in the past few years provided a starting point for this work," he explained. "We know for example that Neisseria meningitidis are equipped with special structures known as pili. These allow the bacteria to adhere to cells of the throat and to multiply and form aggregates there."

The researchers studied the main protein that made up pili, namely pilin. They discovered that it underwent various modifications over time and if a chemical of the phosphoglycerol group became grafted onto the pilin it gave the signal for dissemination.

The researchers next discovered that it was the presence of the gene pptB that enabled the transfer of the phosphoglycerol onto the pilin. This gene only becomes fully functional when the bacteria are in contact with the cells lining the wall of the throat.

Once the gene becomes active and phosphoglycerol is transferred to the pilin, the Neisseria meningitidis loses it ability to aggregate. This causes some of the bacteria to break away and become disseminated. Other areas of the throat are colonised and the bloodstream is invaded.

Having discovered how Neisseria meningitidis enters the bloodstream, the researchers now hope to be able to demonstrate that it invades the brain in the same way, but the ultimate hope is to find molecules that will provide a preventive tool by blocking this dissemination in the first place.