Babies who have acquired four key bacteria in their gut by the age of three months may be protected against asthma, a new study suggests.

The finding by Canadian researchers, published today in Science Translational Medicine, could lead to tests to identify babies most at-risk of developing asthma and even inoculations to prevent its onset.

The study also adds weight to the "hygiene hypothesis" that suggests an obsession with clean home environments has fuelled a dramatic rise in asthma rates across western societies since the 1950s.

For the study the researchers analysed stool samples collected at age three months and one year of 319 children participating in the larger Canadian Healthy Infant Longitudinal Development (CHILD) study.

The study showed lower levels of four specific gut bacteria - Faecalibacterium, Lachnospira, Veillonella and Rothia - in three-month-olds who were later found to be at an increased risk for asthma.

However, differences in levels of these bacteria were negligible by the time children reached one year, meaning the first three months were the critical time period for a baby's developing immune system.

"It shows there's a short, maybe 100-day window for giving babies therapeutic interventions to protect against asthma," said study lead co-author Professor Stuart Turvey, Pediatrics Professor at the University of British Columbia.

However, Professor Turvey, a former Australian Rhodes Scholar, said while the finding was significant there was still much to learn about the bacteria, nicknamed FLAVR.

Potential for probiotic treatments

Professor Turvey said most babies naturally acquired the FLAVR bacteria from their environments, but they were unsure why they would not be in equal levels in some babies.

"These are not particularly well-characterised bacteria so we are not exactly sure where they come from," Professor Turvey said.

"We are trying to understand which bits of the FLAVR are important and if it could possibly be safe to give that to children."

As part of the study, the researchers replicated the work in mice and found an inoculation of FLAVR in newborn mice helped protect them against developing asthma.

This suggested long term they could develop some "probiotic-style treatment" for children that would prevent the onset of asthma, he said.

Professor Turvey said it was likely the first outcome of the study would be to develop a marker for children at the highest risk of asthma.

"In the first couple of months we could test their stool and test for the presence of FLAVR," he said.

He said the study also highlighted the importance of "prudent" use of antibiotics in very young children as the study confirmed previous work that showed a link between antibiotic use in the first year and asthma.

'We need to change our relationship with bacteria'

He also said the study might reveal the mechanism behind the "hygiene hypothesis".

"This idea that exposure to infections in early life protects from asthma and allergic disease has mostly been through epidemiology," he said, pointing to studies of children with pets and those who lived on farms.

"This shows that a likely mechanism for that protection is through the bacteria that children house in their gut."

Professor Turvey said the study showed "we need to change our relationship with bacteria".

"We co-evolved and they are really important for our health as well," he said.

The team was now working with researchers in Ecuador who have a study similar to the Canadian CHILD study to see if the findings can be replicated in another population.