The gastrointestinal microbiome may have a potent influence on the risk of respiratory diseases including asthma, an expert says.

Speaking in an ATS session on the early determinants of respiratory disease Dr Susan Lynch, a microbiologist from the University of California at San Francisco said knowledge of the bacteria, viruses and fungi colonising the body used to be limited to those that could be cultured in a laboratory.

“The advent of new technology has vastly increased our understanding of their contribution to health and disease,” she said.

The microbiome outnumber the 22,000 human genes by about 100 to 1, she told delegates.

“It is now clear that the gastrointestinal microbiome can drive the development of allergic asthma,” she said.

Studies in mice have revealed some of the mechanisms that might be involved. A high fibre diet, for example, has been shown to reduce susceptibility to allergic airway disease by transforming gut microflora into short-chain fatty acids that have strong anti-inflammatory effects.

Recognised risk factors for childhood atopy – such as caesarean section, breastfeeding and maternal antibiotic exposure – were also known to affect the microbiome.

Dr Lynch and her colleagues are examining changes in the gastrointestinal microbiome in early life, commencing with neonatal meconium and tracking how infants accumulate new species during their first year.

Their work is based partly on a Canadian study comparing young children who were ‘atopic wheezers’ with those who had healthy airways.

The research found no difference in the extent of microbial diversity between the two groups, but the wheezy children had marked differences in the dominant organisms within the gut.

The differences were evident at the age of three months but had diminished by 12 months, suggesting that their adverse influence occurred very early in life.