Harmless bacteria may help prevent meningococcal outbreaks

London: Researchers have shown for the first time that nasal drops of harmless bacteria can inhibit a related bug that sometimes causes meningococcal disease.

Meningococcal disease is caused by Neisseria meningitidis, which can infect the lining of the brain and the spinal cord, causing meningitis. Strains of the bacteria can also cause serious bloodstream infections.

N meningitidis can also live silently in a person's nose and throat, without illness. These "colonised" carriers can spread the pathogen to others through close contact.

In the study, researchers placed drops containing low doses of Neisseria lactamica, a related but harmless bacterial strain, into the noses of 149 healthy university students in the UK.

A control group of 161 students received drops of saline instead. Nose swabs were taken at regular intervals over six months and tested for both types of bacteria.

Among students who received the N lactamica drops and became colonised, the harmless bacteria appeared to prevent N meningitidis from colonising the students' throats.

The "good" bacteria also displaced the worrisome pathogen in those who were already carrying it when the study began.

The effect was seen after just two weeks, when the number of students carrying N meningitidis in their upper airway dropped by 9.5 per cent among those who were also colonised by N lactamica using the drops. The effect lasted for at least four months.

"It's the first time that anyone has taken a bug - a friendly bacterium - and has shown that it changes the way that you can become colonised by the meningitis bacterium, Neisseria meningitidis," said study author Robert C Read of the University of Southampton in the UK.

Meningococcal vaccines induce high levels of antibodies in the blood to ward off infection, but current vaccines also limit "carriage" of N meningitidis in the throat, preventing its spread from one person to another.

The drop in carriage seen in this study was faster and more persistent than that seen after vaccination. The harmless bacterial strain was also active against more varieties of N meningitidis.

The findings suggest that N lactamica may one day help suppress meningococcal outbreaks as a bacterial medicine.

The research is published in the journal Clinical Infectious Diseases.