A baby’s diaper may not be the most pleasant thing to look at, but what it contains can provide doctors with a hint about whether that child may develop asthma later in life, thus allowing them to start treating him or her in order to prevent the disease. Researchers have found that four bacteria found in the faeces of a three-month-old infant play a key role in this long-term lung condition affecting 300 million people worldwide.

Previous studies with animals had suggested there was a link between the disease and our gut microbiota but this is the first time the relationship has been demonstrated in humans. Published in Science Translational Medicine, the findings, scientists claim, could help improve risk prediction of the disease and could also lead to the development of probiotic treatments to prevent it.

Led by Brett Finlay, Professor of Microbiology and Biochemistry at the University of British Columbia, scientists first tested 319 children enrolled in the Canadian Healthy Infant Longitudinal Development Study (CHILD) to see whether they were at risk of suffering from asthma. To do so, they carried out an allergy skin test on the infants and also observed if the kids wheezed, as these two symptoms are considered to be key factors that increase asthma risk probability. Twenty-two of those tested were found to be at high risk of becoming asthmatics.

Scientists then analysed the stools of all the infants when they were three months old. Interestingly, they observed that the babies with a higher risk of asthma presented lower levels of four bacteria in their faeces samples in comparison with the infants who did not show any symptoms. Those bacteria were identified as Faecalibacterium, LachnospiraVeillonella and Rothia – known all together as FLVR.

Researchers analysed stool samples once again when the children were one year old and discovered that, by then, the differences in gut microbiota composition between the two groups was smaller. Researchers highlight, therefore, that the presence of these four microbes early in life could play an active role in protecting infants from asthma.

To prove this, the team of scientists carried out a second experiment, this time with rodents. They took germ-free animals and administered stool samples from the asthma-prone babies to them. As expected, the mice developed inflammation in their lungs. However, if the researchers gave them a combination of the FLVR microbes together with the faeces, the rodents’ risk of developing asthma decreased.

For Stuart Turvey, a paediatrician from the University of British Columbia, Vancouver and co-author of the paper, these findings can be useful in predicting, very early on, which children have a high risk of suffering asthma. “Those children could be followed or treated more quickly if they end up with asthma,” he explained during a press conference. The first three months has therefore proven to be a ‘critical window’ in which disruptions in the development of a healthy gut microbiota can lead to asthma.

Our study emphasises that in that first 100 days [of life], the structure of the gut microbiome seems to be very important in influencing the immune responses that cause or protect us from asthma,” added Turvey. He also highlighted that once the children at a heightened risk were identified, they could be treated with a combination of the four bacteria – FLVR – in order to prevent the onset of the respiratory condition.

During the past three decades, asthma cases have risen dramatically, particularly in so-called developed countries, affecting nearly 14% of the child population. For a long time, genetic and environmental factors such as pollution, together with the hygiene hypothesis, were thought to trigger the condition. But, over the last decade studies had already pointed to the fact that microbiota alterations during infancy might be linked to diseases like allergies and asthma.

“Asthma is really on the rise throughout the world in developed countries. There is a lot of evidence that the microbiota may actually play a role in this because of things such as a Caesarean section versus a vaginal delivery increases your risk of asthma; breastfeeding decreases; antibiotics in the first year of life significantly increase incidence; having a pet or living on a farm decrease it. So there are all these sorts of smoking guns to indicate that the microbiota may be involved in this, but there were no experiments to prove it,” explained UBC microbiologist Brett Finlay during a press conference.

As gut microbiota are known to differ in different cultures, researchers have already announced they are repeating the experiment with a larger and more diverse cohort of infants, including children from Ecuador. The aim is to check whether the four bacteria found to be relevant in the first study could be universal key factors.