Study Links Variations in CF Patients’ Airway Bacteria Mix with Their Disease Outcomes

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by Diogo Pinto |

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Researchers have linked variations in the mix of microorganisms in cystic fibrosis patients’ airways to their disease outcomes.

The findings in the journal PLOS One were in an article titled “Fluctuations in airway bacterial communities associated with clinical states and disease stages in cystic fibrosis.

CF patients typically have particular strains of bacterial and fungus in their airways. The usual bacteria suspects include Pseudomonas, Achromobacter, Burkholderia, Haemophilus, Staphylococcus, and Stenotrophomonas.

Other bacteria and fungi also inhabit CF patients’ airways, however. These include anaerobic species that do not need oxygen to grow and spread.

Not only do the microbial communities in CF patients’ airways vary by type of microorganism, but also in the relative abundance of each species.

Researchers decide to see if the prevalence and relative abundance of typical CF pathogens and anaerobic microorganisms play a role in the severity of patients’ disease and their lung function.

They analyzed 631 sputum samples collected over 10 years from 111 patients.

The team classified the stage of patients’ disease on the basis of their lung function scores. The yardstick they used was forced expiratory volume in one second, or FEV1. They considered an early stage of the disease to be an FEV1 score higher than 70, an intermediate stage a score of 40 to 70, and an advanced stage a score lower than 40.

Researchers classified disease aggressiveness — mild, moderate or severe — on the basis of change in FEV1 relative to age.

They discovered a link between variations in the prevalance of the six typical CF pathogens, plus nine anaerobic species, and changes in a patient’s disease stage and lung function. One finding was an increase in the relative abundance of anaerobic microorganisms when patients were experiencing pulmonary exacerbations before  antibiotic treatment, and a decrease during treatment and patients’ post-treatment recovery phase.

“Both bacterial community diversity and the relative abundance of anaerobes increased during exacerbation of symptoms (prior to antibiotic treatment),” the researchers wrote, although they added that “community diversity and the relative abundance of anaerobic species decreased during antibiotic treatment.”

When the stage of the disease advanced, Pseudomonas was the most dominant group in more than half of the samples. Another finding was that the proportion of samples in which an anaerobic species was the dominant group decreased from about 30% to 12% as the disease stage advanced.

Among the 24 patients studied for disease aggressiveness, 14 showed mild severity, six had moderate severity, and four had severe forms of the disease. Patients with moderate or severe disease aggressiveness seemed to lose anaerobic species earlier than those with a mild disease.

The stage of the disease “must be taken into account in interpreting results of studies assessing CF airway communities,” the researchers wrote. “Our results also highlight the importance of disease aggressiveness and the utility of a long-term perspective.

“A better appreciation of [micro-organism] community dynamics in the context of patients’ health status is an important step in advancing our understanding of the role airway microbiota play in pulmonary exacerbations and disease progression in CF,” the team concluded.