Study on antibiotics and the microbiome in asthmatic patients

The airway physiology and the bacterial burden of the airways, skin and gastrointestinal tracts do not change meaningfully over time in asthmatic patients who are exposed to an antibiotic, the Irish Thoracic Society Annual Scientific Meeting was told.

Presenting on antibiotics and the microbiome in asthmatic patients, Dr Orla O’Carroll from Connolly Hospital, Dublin, said that the respiratory microbiome is a relatively new concept in terms of research.

“In fact the Index study, which proved for the first time that the lungs were not sterile as previously thought, occurred only in 2009. Since then there’s been an explosion of interest in the area,” she said.

“Although some key characteristics, particularly pertaining to asthma remain undiscovered.

“What we do know is that the microbiome of the asthmatic airway is significantly altered in asthmatic patients compared with controls, or those with other disease processes.”

This alternation seems to be associated with some altered clinical parameters, such as airway hyper-responsiveness and with response to various treatment strategies.

In contrast, researchers knew more about the gut and skin biome, which have benefited from a longer time of extensive research.

“And we do know that both of them are implicated with asthma,” said Dr O’Carroll.

“If patients have lower gut diversity in infancy and early life, there is a higher risk of developing asthma in later life.”

The microbiome of the skin is also implicated in atopic dermatitis development, a condition closely related to asthma. However, it is unknown how these three microbiome compartments interact in asthmatics. This was one of the key questions the researchers sought to untangle, Dr O’Carroll said.

“We also don’t know how they interact longitudinally and we are not sure what effect treatments, such as antibiotics and steroids, have on them.”

The aim of the study, which was carried out alongside Imperial Hospital, London’s genomics lab, was to concurrently assess the microbiome in multiple systems in asthmatic patients, to integrate this assessment with detailed measures of airway physiology and to assess how the microbiome change longitudinally in response to an antibiotic.

The population was drawn from the patients attending an asthma clinic in Blanchardstown. They were excluded if they had confounding occupations, were using systematic steroids or biological treatments for their asthma or had BMI < 30. Patients were also only considered to be asthmatic if they demonstrated objective evidence of airflow limitation.

If patients were eligible they were then consented and underwent further detailed physiological assessment, including measurement of fractional exhaled nitric oxide (FeNO).

Bronchoscopy was the next intervention carried out. Patients had multiple lung brush samples taken as well as endobronchical samples. Furthermore, faecal samples and skin swab samples were collected. Patients were then given a 10-day course of oral levofloxacin.

After bronchoscopy and antibiotic treatment, patients returned to the clinic at four weeks and six weeks, at which time skin swabs, throat swabs, and faecal samples were repeated. A full lung function assessment was also repeated and they underwent second bronchoscopy at eight weeks.

At the lab in London, all biological samples underwent DNA extraction and precipitation, spectrophotometry, and 16S rRNA analysis

“The 16S rRNA copy count per ul can be used as an imperfect but acceptable proxy for bacterial burden of each given sample,” said Dr O’Carroll.

“It’s particularly useful in cases like this where it’s a longitudinal comparative assessment.”

Some 13 patients successfully completed the study protocol, and there was an even spread between male and female patients. All patients were non-smokers and had never smoked and were medicated for asthma to varying degrees. They were also medicated for other related conditions, such as rhinitis, and other non-related conditions mostly hypertension.

The patients were stratified into genotreatment groups via medication use; this revealed that most were at the moderate end of the disease spectrum.

The key finding of the study was that airway physiology and the bacterial burden of the airways, skin and gastrointestinal tracts do not change meaningfully over time in asthmatic patients exposed to an antibiotic.

“The value of this study is we believe it is the first concurrent assessment of these different microbiome systems in a longitudinal sense,” Dr O’Carroll said.

“It was a difficult study protocol for subjects, but it showed that it is possible.”

She acknowledged that there were limitations to the study, including the small sample size, which was mostly due to the intensity of the trial protocol.

There was no DNA sequence data available as of yet to complete the picture but this should be forthcoming, she said.

Dr O’Carroll added that it was very difficult to control the confounders in the microbiome analysis.

In conclusion, the researchers found that altered airway physiology defines asthma and that the microbiome is altered in asthma.

The airway physiology and bacterial burden of the lungs, skin, and gut seem to remain constant over times, despite interventions.

The functional impacts of these relationships are largely unknown and there is a need for further studies to define other characteristics of the system, she said.

The researchers believed that DNA sequence data will complete some of these observations.