US researchers have identified a cluster of nose and throat bacteria that made their hosts less likely to get flu.

The researchers from the University of Michigan (UM) looked at samples of nose and throat bacteria and used DNA sequencing to identify which bacteria were present. Analysing the bacterial composition across all samples, they found five clusters.

After taking into account other known factors that could affect an individual's susceptibility to influenza, such as age, exposure to tobacco, crowded household and flu vaccination, the researchers then looked to see if individuals with a given cluster were less likely to get influenza.

"We looked at who had which cluster and whether it makes a difference on whether they got influenza, and it does," said lead author Betsy Foxman, Professor at UM. "That's the exciting thing about it. It tells us if you have this bacterial community, you have lower risk for getting the flu. That's big news because it really hasn't been shown before."

However, the findings published in PLOS ONE journal also bring new questions. "Is it really possible to push someone's microbiome in a way that would make a difference? Is it possible that we could tell people - 'Here's your microbiome pill?'" Foxman said, adding that "It's a very long road and we're at the beginning."

Researchers hope that similar studies can be done in a different population and possibly follow them longer for secondary bacterial infections. "We know we are always going to need new antibiotics but this way we could hold on to them longer and, presumably, if we could intervene in this way there would be fewer side effects," Foxman said.

For the study, the team enrolled 717 participants from 144 households. Household members of individuals with confirmed influenza were recruited for the study and followed for 13 days or until they developed influenza, whichever came first. They included only the 537 individuals who tested negative for influenza at the beginning of the study.