Anaerobic Bacteria in Cystic Fibrosis Airways Associated With Milder Disease

In patients with cystic fibrosis (CF), the presence of anaerobic bacteria is associated with milder disease, suggesting that eradicating anaerobes may not be beneficial, according to the results of a study published in the European Respiratory Journal.

The role of anaerobic bacteria in CF lower airways disease is not well understood. Of note, although in vitro studies have shown that anaerobes release virulence factors, including both proteases and pro-inflammatory short chain fatty-acids, suggesting that anaerobes may be pathogenic in CF, in vivo molecular studies have demonstrated that greater anaerobe diversity is associated with milder disease.

Marianne S. Muhlebach, MD, of the Department of Pediatrics, University of North Carolina at Chapel Hill in North Carolina, and colleagues, set out to explore the correlation of strict anaerobes with disease severity in CF across age groups. They analyzed respiratory samples from 3 CF centers using extended culture methods. Participants between ages 1 and 69 who were clinically stable provided sputum samples or bronchoalveolar lavage (BAL).

The study enrolled 255 participants. A total of 200 sputum and 55 BAL samples were collected. The investigators cultured 18 anaerobic and 39 aerobic genera from 59% and 95% of samples, respectively. Of the 57 genera, 16 had ≥5% prevalence across the 3 centers. The prevalence and quantities of all bacteria were lower in BAL than they were in sputum.

The focus was on strict anaerobes, so Pseudomonas and Staphylococcus, which can also grow anaerobically, were classified as aerobes for the purposes of this study. Of note, the prevalence of anaerobes and Streptococcus decreased from early childhood to early adulthood, which is also a time when many patients with CF experience worsening disease.

The researchers suggested that the presence of CF lower airway oral bacteria is likely the result of aspiration and impaired mucociliary clearance in CF, which enhances retention of aspirated flora in an anaerobic environment.  A higher prevalence of anaerobic bacteria was also associated with higher lung function, less use of antibiotics, increased body mass index, pancreatic sufficiency, and no requirement for insulin, as well as milder disease. In contrast, the presence of Pseudomonas was associated with worse nutrition and the F508del genotype.

The investigators cautioned against the targeted eradication of anaerobic bacteria in sputum- producing patients with CF.

Reference

Muhlebach MS, Hatch JE, Einarsson GG, et al. Anaerobic bacteria cultured from CF airways correlate to milder disease—a multisite study [published online July 11, 2018]. Eur Respir J. doi:10.1183/13993003.00242-2018