How an Innocuous Bacteria Lots of Us Have Turns into Deadly Meningitis & Sepsis

How can bacteria that lives in the throat of 10%–35% of people—without causing an infection—cause life-threatening meningitis and sepsis in others?

A new study published in the journal PLOS Pathogens by scientists from Stockholm University in Sweden, led by Sara Sigurlásdóttir, reported finding the process Neisseria meningitidis bacteria use to move from a person's throat to their brain, where they set up a serious brain infection.

Part of the path N. meningitidis takes to causing menigitis is already known. In the first critical step, the bacteria must colonize, i.e., set up an infection, in the mucosal layer of the upper throat. Then, somehow, the tiny colonies disperse. They spread out rapidly and gain entry to the blood by invading the mucosal lining of the throat. From there, they infect the blood or travel to the brain to set up bacterial meningitis.

Bacterial dispersal in high lactate concentrations.

Looking for something inside a human cell that might trigger this process, the scientists found that lactate, a chemical produced from glucose (sugar) metabolism could signal this process to start.

They found that high concentrations of lactate can initiate dispersal of bacterial colonies into microcolonies. From there, the Neisseria can act as single cells and cross the lining of the throat and respiratory tract. This movement requires the presence of live epithelial cells—the cells lining the respiratory tract— but not direct contact between cells and bacteria.

Once they cross that barrier, the bacteria continue on to the brain to cause meningitis.

Neisseria Meningitis

People who live in close contact with someone infected with N. meningitidis and might share saliva by coughing and kissing, like with families, in college dorms, and in other close relationships, are at risk for being infected, too. It strikes infants, children, and young adults more often than other ages.

The bacteria is not considered to be extremely contagious, and still some people will carry the bacteria in their throat without developing an infection in their throat, blood, or brain.

For those that become colonized and have the bacteria disperse, and as N. menigitidis moves into the blood, they may experience fever, fatigue, vomiting, chills, aches, rapid breathing, and diarrhea. They may also develop a dark purple rash. Sometimes, limbs that develop this rash need to be amputated because the bacteria has killed the tissue.

Once the bacteria travels to the brain, patients often complain of a stiff neck, fever, headache, sensitivity to light, and confusion. It's critical to seek medical attention immediately for any of these symptoms.

Your doctor will treat meningitis with antibiotics, but may need to examine your spinal fluid to make an accurate diagnosis. Time is of the essence, though, because patients who start antibiotics quickly have a better chance of survival.

Despite antibiotic treatment, 10%–15% of people with this meningitis will die. Of those who survive, up to 20% are left with long-term disabilities, like loss of limb(s), deafness, nervous system problems, or brain damage.

Rates of meningitis in US

For unknown reasons (but thankfully), rates have been declining since 2000. That was of little solace when we didn't know and couldn't tell who would develop infection with N. meningitidis that would turn into meningitis.

The discovery by Sigurlásdóttir and colleagues may have answered that question. It may be the first step toward identifying people at risk for this potentially lethal meningitis and finding a way to prevent it.

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Cover image by James Volk/CDC