Composition of airway bacterial community correlates with chest HRCT in adults with bronchiectasis

Airway total bacterial density, microbiota community composition and relationship with clinical parameters in bronchiectasis

BACKGROUND AND OBJECTIVE

This study explored the relationship between total bacterial density, airway microbiota composition and clinical parameters in bronchiectasis. We determined changes with time during clinical stability and following antibiotic treatment of a pulmonary exacerbation.

METHODS

We conducted a multicentre longitudinal cohort study of UK participants with CT confirmed bronchiectasis. Sputum samples and clinical parameters [FEV1% predicted, lung clearance index, C-reactive protein, white cell count and Quality of Life] were collected when participants were clinically stable and pre/post-antibiotic treatment of an exacerbation. Total bacterial density and microbiota community composition was measured by quantitative polymerase chain reaction and sequencing of the V4 region of bacterial 16S rRNA, respectively.

RESULTS

Among 105 participants at baseline, 65 (62 %) were female with a mean age of 65 years and FEV1 at 69 % predicted. In participants who remained clinically stable (n = 15), no significant changes were observed in bacterial density, microbiota diversity, richness, evenness, and dominance (p = 0.30, 0.45, 0.54, 0.23 and 0.43; respectively) across four time points over a 1-year period. Similarly, for participants with paired pre/post-antibiotic treatment samples (n = 19), no significant changes were observed (p = 0.30, 0.46, 0.44, 0.71 and 0.58; respectively). However, considerable fluctuation in community composition between samples was apparent for most patients. Total bacterial density and microbiota composition did not correlate with clinical parameters at baseline (n = 75).

CONCLUSIONS

Stability in bacterial density and microbiota diversity, richness, evenness and dominance was observed over time at a population level but considerable fluctuation was apparent in samples from individual patients.

Bronchiectasis

Bronchiectasis is a final common pathway of a wide variety of underlying conditions including infectious, autoimmune, allergic, genetic and inflammatory conditions. Patients experience a chronic disease with variable clinical symptoms and course, but most experience cough, sputum production and recurrent exacerbations. Symptoms of bronchiectasis lead to poor quality of life and exacerbations are the major driver of morbidity and mortality. Patients are often chronically infected with bacteria with the most common being Pseudomonas aeruginosa and Haemophilus influenzae. Treatment of bronchiectasis includes standardised testing to identify the underlying cause with targeted treatment if immune deficiency, allergic bronchopulmonary aspergillosis or non-tuberculous mycobacterial infection, for example, are identified. Airway clearance is the mainstay of therapy for patients with symptoms of cough and sputum production. Frequently exacerbating patients may benefit from long term antibiotic or mucoactive therapies. Bronchiectasis is a heterogeneous disease and increasingly precision medicine approaches are advocated to target treatments most appropriately and to limit the emergence of antimicrobial resistance.

Pseudomonas aeruginosa in bronchiectasis: infection, inflammation, and therapies

Introduction: Bronchiectasis is a chronic endobronchial suppurative disease characterized by irreversibly dilated bronchi damaged by repeated polymicrobial infections and predominantly, neutrophilic airway inflammation. Some consider bronchiectasis a syndromic consequence of several different causes whilst others view it as an individual disease entity. In most patients, identifying an underlying cause remains challenging. The acquisition and colonization of affected airways by Pseudomonas aeruginosa represent a critical and adverse clinical consequence for its progression and management.Areas covered: In this review, we outline clinical and pre-clinical peer-reviewed research published in the last 5 years, focusing on the pathogenesis of bronchiectasis and the role of P. aeruginosa and its virulence in shaping host inflammatory and immune responses in the airway. We further detail its role in airway infection, the lung microbiome, and address therapeutic options in bronchiectasis.Expert opinion: P. aeruginosa represents a key pulmonary pathogen in bronchiectasis that causes acute and/or chronic airway infection. Eradication can prevent adverse clinical consequence and/or disease progression. Novel therapeutic strategies are emerging and include combination-based approaches. Addressing airway infection caused by P. aeruginosa in bronchiectasis is necessary to prevent airway damage, loss of lung function and exacerbations, all of which contribute to adverse clinical outcome.

The airway microbiome in COPD, bronchiectasis and bronchiectasis-COPD overlap

OBJECTIVE

To review the airway microbiome in chronic obstructive pulmonary disease (COPD), bronchiectasis and bronchiectasis-COPD overlap (BCO).

DATA SOURCE AND STUDY SELECTION

Relevant studies were selected from PubMed, Google scholar, EMBASE and Web of Science. All studies involving human microbiomes, published in the English language, and using the search terms "COPD", "Chronic Obstructive Pulmonary Disease", "Bronchiectasis", "BCO" or "Bronchiectasis and COPD overlap", AND "microbiome", "mycobiome" or "metagenomics" were included.

RESULTS

Despite variability in sampling methods and specimen types used, microbiome composition remains relatively comparable in COPD and bronchiectasis with prominence of Proteobacteria, Firmicutes and Bacteroidetes. Alterations to airway microbiomes occur in association to disease severity and/or exacerbations in COPD and bronchiectasis. Decreased alpha diversity and Haemophilus-predominant microbiomes are associated with poorer survival in COPD, while, in bronchiectasis, Pseudomonas-predominant microbiomes demonstrate high exacerbation frequency and greater symptom burden while Aspergillus-dominant mycobiome profiles associate with exacerbations. The role of the microbiome in BCO remains understudied.

CONCLUSION

Use of next-generation sequencing has revolutionised our detection and understanding of the airway microbiome in chronic respiratory diseases such as COPD and bronchiectasis. Targeted amplicon sequencing reveals important associations between the respiratory microbiome and disease outcome while metagenomics may elucidate functional pathways. How best to apply this information into patient care, monitoring and treatment, however, remains challenging and necessitates further study.

Lung clearance index in healthy volunteers, measured using a novel portable system with a closed circuit wash-in

Introduction

Lung clearance index (LCI) is a sensitive measure of early lung disease, but adoption into clinical practice has been slow. Challenges include the time taken to perform each test. We recently described a closed-circuit inert gas wash-in method that reduces overall testing time by decreasing the time to equilibration. The aim of this study was to define a normative range of LCI in healthy adults and children derived using this method. We were also interested in the feasibility of using this system to measure LCI in a community setting.

Methods

LCI was assessed in healthy volunteers at three hospital sites and in two local primary schools. Volunteers completed three washout repeats at a single visit using the closed circuit wash-in method (0.2% SF₆ wash-in tracer gas to equilibrium, room air washout).

Results

160 adult and paediatric subjects successfully completed LCI assessment (95%) (100 in hospital, 60 in primary schools). Median coefficient of variation was 3.4% for LCI repeats and 4.3% for FRC. Mean (SD) LCI for the analysis cohort (n = 53, age 5–39 years) was 6.10 (0.42), making the upper limit of normal LCI 6.8. There was no relationship between LCI and multiple demographic variables. Median (interquartile range) total test time was 18.7 (16.0–22.5) minutes.

Conclusion

The closed circuit method of LCI measurement can be successfully and reproducibly measured in healthy volunteers, including in out-of-hospital settings. Normal range appears stable up to 39 years. With few subjects older than 40 years, further work is required to define the normal limits above this age.