Green BJ, Wiriyachaiporn S, Grainge C, Rogers GB, Kehagia V, Lau L, Carroll MP, Bruce KD, Howarth PH. Potentially pathogenic airway bacteria and neutrophilic inflammation in treatment resistant severe asthma.
PLoS One 2014;
9:e100645. [PMID:
24955983 PMCID:
PMC4067344 DOI:
10.1371/journal.pone.0100645]
[Citation(s) in RCA: 227] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Accepted: 05/29/2014] [Indexed: 01/06/2023] Open
Abstract
Background
Molecular microbiological analysis of airway samples in asthma has demonstrated an altered microbiome in comparison to healthy controls. Such changes may have relevance to treatment-resistant severe asthma, particularly those with neutrophilic airway inflammation, as bacteria might be anticipated to activate the innate immune response, a process that is poorly steroid responsive. An understanding of the relationship between airway bacterial presence and dominance in severe asthma may help direct alternative treatment approaches.
Objective
We aimed to use a culture independent analysis strategy to describe the presence, dominance and abundance of bacterial taxa in induced sputum from treatment resistant severe asthmatics and correlate findings with clinical characteristics and airway inflammatory markers.
Methods
Induced sputum was obtained from 28 stable treatment-resistant severe asthmatics. The samples were divided for supernatant IL-8 measurement, cytospin preparation for differential cell count and Terminal Restriction Fragment Length Polymorphism (T-RFLP) profiling for bacterial community analysis.
Results
In 17/28 patients, the dominant species within the airway bacterial community was Moraxella catarrhalis or a member of the Haemophilus or Streptococcus genera. Colonisation with these species was associated with longer asthma disease duration (mean (SD) 31.8 years (16.7) vs 15.6 years (8.0), p = 0.008), worse post-bronchodilator percent predicted FEV1 (68.0% (24.0) vs 85.5% (19.7), p = 0.025) and higher sputum neutrophil differential cell counts (median (IQR) 80% (67–83) vs 43% (29–67), p = 0.001). Total abundance of these organisms significantly and positively correlated with sputum IL-8 concentration and neutrophil count.
Conclusions
Airway colonisation with potentially pathogenic micro-organisms in asthma is associated with more severe airways obstruction and neutrophilic airway inflammation. This altered colonisation may have a role in the development of an asthma phenotype that responds less well to current asthma therapies.
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