Like a sprawling urban city, certain neighborhoods of the human body support different communities of microbes. And many of these are good guys; the microbes in our gut help us digest food, for example, whereas those on our tongue and skin can guard against invading pathogens. Now, researchers have found beneficial bacteria in our nose as well. This “nasal microbiome” may guard against chronic sinus inflammation or even allergies.
The study is “an important gateway” to recognizing bacteria’s protective qualities in a new part of the body, says Maria Marco, a microbiologist at the University of California, Davis, who was not involved with the work. “There’s been some work done in the past, but this is the first study that goes in depth.”
To conduct the study, researchers co-led by Sarah Lebeer, a microbiologist at the University of Antwerp, went sleuthing for bacteria in the noses of 100 healthy people. Then, the scientists compared the microbes they found with those from hundreds of patients with chronic nasal and sinus inflammation.
Of the 30 most common types of microbes the team discovered, one group stood out: antimicrobial and anti-inflammatory bacteria called Lactobacillus. These were up to 10 times more abundant in the noses of healthy people, the researchers publish today in Cell Reports.
Lactobacilli usually thrive in oxygen-poor areas, so Lebeer was surprised to see them in an organ flush with fresh air. But a closer look revealed that the particular strain her team found in human noses has special genes called catalases that safely neutralize oxygen—a rarity among other lactobacilli. “They seem to have adapted to that environment,” Lebeer says.
Under a microscope, the researchers could also see tiny, hairlike appendages called fimbriae that anchor the bacteria to the nose’s inner surface. Lebeer thinks the microbes may also use the hairs to bind to receptors on skin cells inside the nose, prompting the cells to close like a trap door. With fewer cells open, allergens and harmful bacteria have a harder time getting inside them.
But on its own, the presence of Lactobacillus in healthy people is not enough to say it guards against disease, Lebeer admits. Whether the microbes are protective is also difficult to test in animal models such as mice, which have very different noses.
And some experts aren’t convinced that the lactobacilli the team found are uniquely adapted to the human nose. The mouth is also home to millions of lactobacilli, notes Jens Walter, a microbiologist at University College Cork, and these could end up in the nose through sneezing. The results of the study are “the right first steps,” Walter says, but he would like to see more research to reinforce their novelty and potential benefits.
Ultimately, Lebeer hopes to develop therapeutics using nasal probiotics. Sinus conditions have few treatments, and chronic conditions that must be continually treated raise the risk of a bacteria becoming resistant to antibiotics. Introducing beneficial strains of bacteria lacking antibiotic resistance genes would be a lower risk solution, she says.
As a first step, Lebeer has developed a nasal spray containing the Lactobacillus microbes her team isolated. The lactobacilli safely colonized the patients with no ill effects.
sciencemag.org, 27 May 2020