Bacteria can cause — or prevent — wheezing in young children

Particular combinations of bacteria found in dust at day care facilities have been linked to wheezing in young children, according to a study presented at the European Respiratory Society International Congress in Milan. In children under three years old, wheezing is considered to be an early sign of asthma.

“We find mixtures of different bacteria and other microbes living everywhere — outside, inside our homes, on our skin and even inside our bodies,” said Dr Annabelle Bédard, a researcher at Inserm (the French National Institute of Health and Medical Research). “These communities of bacteria, known as microbiota, can have beneficial or harmful effects on our health.

“Young children will come into contact with the bacteria living in day care centres via their skin and mouths and by breathing them in. So, we might expect this exposure to have an impact on children’s developing lungs via the different microbiota that arise in children’s airway, gut or skin.”

Bédard and her fellow researchers used an adapted vacuum cleaner to collect samples of dust from the floor of 103 different day care settings in the Paris region. They used genetic analysis in the laboratory to identify the different types of bacteria found in each sample. At the same time, they asked the parents of 515 children attending the day care facilities whether their children experienced any respiratory symptoms, such as wheezing.

Based on the types of bacteria found in the samples, the researchers were able to group mixtures of microbiota from the day care centres into four broad categories. One of these categories, in which two different bacteria called Streptococcus and Lactococcus were dominant, was linked with an increase in the risk of wheezing, compared with the more common category (a mixture of Streptococcus, Neisseria and Haemophilus bacteria).

“Our research suggests that there are differences in the risk of recurrent wheezing depending on mixtures of bacteria in the day care setting,” Bédard said.

“We now need to understand what factors influence this bacterial community, for example how the rooms are cleaned and ventilated, and indoor air quality. This, along with future findings from other studies, could help understand how to improve conditions and inform public health strategies for preventing chronic respiratory diseases such as asthma in children.”

The good news, according to a separate study presented at the congress, is that babies and young children with more mature microbiota present in their gut are less likely to develop allergy-related wheezing or asthma. Babies already have some microbiota from their mothers when they are born, which increase in diversity and maturity as babies grow older and are exposed to more different types from sources such as other children, animals and different foods.

The Barwon Infant Study (BIS) recruited 1074 babies between 2010 and 2013, with researchers following the babies as they grow. For this current study, Deakin University’s Dr Yuan Gao and her colleagues at looked at the bacteria present in faecal samples collected from the BIS babies one month, six months and one year after birth. At the one-year and four-year postnatal reviews, the investigators asked the parents to report on whether their children had developed allergy-related wheeze or asthma in the previous 12 months. They also did skin-prick tests to see if the children had allergic reactions to any of 10 foods and any airborne substances that can trigger an allergic response, such as rye grass or dust.

In a randomly selected subgroup of 323 children, the BIS team used a DNA sequencing technique to identify and characterise the gut microbiota. They calculated ‘microbiota-by-age z-score’ (MAZs), which is a mathematical estimate of the maturity of the children’s gut microbiota.

“We found that if babies had more mature gut microbiota when they were one year old, they were less likely to have an allergy-related wheeze at one and four years old,” Gao said. “If MAZ increased within a certain range, known as standard deviation, it halved the risk of allergy-related wheeze at both these ages. In other words, the more mature the gut microbiota, the less likely were the children to have allergy-related wheeze. We did not find a similar association with MAZ scores at one or six months.”

The mechanisms by which mature gut microbiota contribute to preventing allergy-related disease are not yet completely understood. Gao stated, “Given the complex origins and development of both gut microbiota and the infant immune system, it is likely that the protective effect of a healthy gut microbiota occurs as a result of communities of bacteria acting in multiple different ways, rather than via one particular mechanism.

“We hope that by understanding how the gut microbiota improves the immune system, new ways of preventing allergy-related disease such as asthma can be developed. For instance, it might be possible to suggest ways of advancing the maturation of gut microbiota in early life, which would lead to fewer children developing asthma and other allergy-related diseases in the future.”

The researchers are now planning to recruit 2000 children from Australia and New Zealand to a new clinical trial, called ARROW, to see whether giving young children a mixture of dead bacteria, taken orally, can protect them from wheezing illnesses or asthma by boosting a healthy immune response to viral infections. According to Gao, “ARROW has the potential to dramatically improve the health of children with recurrent wheeze and asthma.”

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