CHICAGO, Dec. 16 (Xinhua) -- There is a link between bacteria that live in the upper airway and the severity of asthma symptoms among children with mild to moderate asthma, according to a study published Monday.

The study raised the possibility that the airway's microbiome could have a causal role in the severity of asthma symptoms, paving the way for future studies to discover whether altering the types of bacteria that live in the upper airway could help patients with asthma.

Led by Washington University School of Medicine in St. Louis, the study was conducted in conjunction with a clinical trial involving 214 children aged 5 to 11 with mild to moderate asthma.

The researchers found that children who experienced early warning signs that their asthma was going to flare up were more likely to have bacteria associated with disease, including Staphylococcus, Streptococcus and Moraxella bacterial groups living in their upper airways.

In contrast, airway microbes dominated by Corynebacterium and Dolosigranulum bacteria were associated with periods of good health, when asthma was well-controlled.

The researchers also found that children whose airway microbial communities switched from being dominated by Corynebacterium and Dolosigranulum bacteria to being dominated by Moraxella bacteria were at the highest risk of worsening asthma symptoms compared with children whose microbial communities made any other kind of shift.

"Our data demonstrated a rapid change of the airway microbiome in the children who transitioned from respiratory health to disease," said Yanjiao Zhou, the paper's first author.

During the clinical trial, the researchers also collected nasal mucus samples from the children to study their upper airway microbiomes. Samples were collected at the beginning of the trial, when all of the participants had controlled asthma, as well as at the first early signs that asthma control was slipping.

In the next step, the researchers plan to conduct studies in mice with carefully controlled airway microbiomes to see if they can uncover a causal role for bacteria in asthma severity. In addition, such experiments could allow them to test different interventions that might deliberately alter the upper airway bacteria in a way that could be protective.

In the United States, more than 6 million children under age 18, or about one in 12, have asthma. It is the leading chronic pediatric disease and the No. 1 reason for missed school days, according to the Asthma and Allergy Foundation of America.

The study, being part of AsthmaNet, a national network of medical centers conducting asthma research funded by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health (NIH), was published in the journal Nature Communications. Enditem

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