A child with a characteristic meningitis rash

The discovery could lead to new ways of treating the disease.

There are two main types of bacterial meningitis, meningococcal and pneumococal.

Meningococcal meningitis is the most common in the UK, with between 2,500 and 3,000 cases.

Most do not cause lasting damage, but, in a few cases, sufferers may die.

Docking

Scientists know which bacteria cause meningitis, but until now, they have not known how that happens.

They needed to find out how they get through the blood-brain barrier.

Once bacteria have got through that, they can easily get into the meninges, membranes which surrounds the brain and the spinal cord.

An international team of researchers followed the progress of the bacterium E.coli in laboratory tests.

Structures on the bacterium called ligands latch on to receptors on cells in the barrier, docking like a spaceship.

This allows them to hitch a lift through the barrier and reach the meninges.

'Important step'

Professor Kwang Sik Kim of John Hopkins University, Baltimore, USA who led the research, told BBC News Online: "We knew which bacterium cause meningitis, but the mechanism was completely unknown.

"If we are to develop new treatments such as immunotherapy, or vaccines that can prime the body to prevent the bacteria from invading, we need to fully understand how these bacteria work.

"This investigation has taken an important step down that path.

"It could provide opportunities to provide serious infection because bacterial meningitis is still a very serious cause of mortality."

Linda Glennie, head of research for the Meningitis Research Foundation, said: "This is the fundamental sort of research that very often provides the key to new therapies or vaccines."

Vaccines

There are three main strains of meningococcal meningitis - A, B and C.

In the UK, a vaccine to protect against meningitis C is given to babies. All children have also been offered the jab.

A vaccine exists for the rarer meningitis A, but it is not effective for young children, the age group most at risk.

However, there is no vaccine for meningitis B, which accounts for two thirds of cases in Britain and kills 200 a year.

It is harder to find a vaccine for this strain because there are a number of different types of menigitis B circulating.