The Airway Microbiome and Disease

doi:10.1378/chest.12-2854

Chest

Volume 144, Issue 2, August 2013, Pages 632-637

https://doi.org/10.1378/chest.12-2854 Get rights and content

Although traditionally thought to be sterile, accumulating evidence now supports the concept that our airways harbor a microbiome. Thus far, studies have focused upon characterizing the bacterial constituents of the airway microbiome in both healthy and diseased lungs, but what perhaps provides the greatest impetus for the exploration of the airway microbiome is that different bacterial phyla appear to dominate diseased as compared with healthy lungs. As yet, there is very limited evidence supporting a functional role for the airway microbiome, but continued research in this direction is likely to provide such evidence, particularly considering the progress that has been made in understanding host-microbe mutualism in the intestinal tract. In this review, we highlight the major advances that have been made discovering and describing the airway microbiome, discuss the experimental evidence that supports a functional role for the microbiome in health and disease, and propose how this emerging field is going to impact clinical practice.

Section snippets

The Airway Microbiome in Health and Disease

The origin of the airway microbiome is yet to be delineated. Endogenous flora from the intestines and the oropharynx, and/or environmental microbes could provide the initial seeding source, or, most likely, a continued source of bacteria (Fig 1). A study by Charlson et al⁷ suggested that the bacterial species detected in the lower respiratory tract of healthy individuals likely originated from microaspiration and reflected the microbiome detected in the upper respiratory tract. Certainly, it is

A Functional Role for the Airway Microbiome?

In spite of a growing bulk of literature describing the airway microbiome in different disease settings, the evidence for its function is still limited. Studies using axenic (germ-free) mice have the potential to address these questions, since these mice are completely sterile. Thus, in theory, future studies could selectively reconstitute the intestinal or airway microbiome and dissect their relative roles.

Some of the first studies to address the importance of the microbiota in allergic airway

What Can We Learn From Other Tissues?

There is a wealth of information available describing host-microbe interactions in the intestine. As mentioned earlier, species diversity is clearly linked to health, while limited diversity is associated with IBD.11, 12 Moreover, certain bacterial species have been linked with the differentiation of inflammatory or regulatory T cells in the intestine.²⁴ Thus, placing the respiratory literature into the context of what is known for the intestine, there already are many parallels. This does

Implications for Clinical Practice

As the outgrowth of certain bacteria is associated with disease severity in CF and COPD,5, 9, 10, 13 this could be used as an indicator for timely clinical intervention and successful disease management. Moreover, the presence of specific bacterial markers such as nucleic acids, proteins, or metabolites could be more sensitive than routine diagnostics and may also precede clinical manifestation of disease. But the ultimate goal would encompass harnessing the understanding of the microbial

Conclusion

On the basis of multiple studies from different international laboratories, the existence of the airway microbiome is now firmly established. Clearly, the field is still in its infancy, and key questions remain to be answered—most notably, what is its function and how can we use it to prevent or treat chronic lung diseases? Is a “pathogenic” microbiome the basis for exacerbations of asthma and COPD? Does it provide the seed for secondary infections? Is there a link between the intestinal

Acknowledgments

Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

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An important component to consider is the well-established connection between respiratory outcomes, particularly atopic conditions like asthma, and respiratory microbial communities, including those that colonize the nose and upper respiratory tract. Modifications and disturbances to those communities, both microbial populations generally and respiratory pathogens specifically, are involved in the pathogenesis of respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), and bronchitis (Dickson et al., 2016; Marsland et al., 2013). More recently, evidence suggests that chemical exposure interactions with the microbiome may lead to altered health statuses.
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Chest

Translating Basic Research into Clinical PracticeThe Airway Microbiome and Disease

Section snippets

The Airway Microbiome in Health and Disease

A Functional Role for the Airway Microbiome?

What Can We Learn From Other Tissues?

Implications for Clinical Practice

Conclusion

Acknowledgments

Immunity

Chest

Ann Allergy Asthma Immunol

Interactions between the microbiota and the immune system

Science

Unravelling the pathogenesis of inflammatory bowel disease

Nature

Gut microbiome, obesity, and metabolic dysfunction

J Clin Invest

Structure, function and diversity of the healthy human microbiome

Nature

Disordered microbial communities in asthmatic airways

PLoS ONE

Rhinovirus infection induces degradation of antimicrobial peptides and secondary bacterial infection in chronic obstructive pulmonary disease

Am J Respir Crit Care Med

Topographical continuity of bacterial populations in the healthy human respiratory tract

Am J Respir Crit Care Med

Asthma-associated differences in microbial composition of induced sputum

J Allergy Clin Immunol

Quantitative analysis of the human airway microbial ecology reveals a pervasive signature for cystic fibrosis

Sci Transl Med

Analysis of the lung microbiome in the “healthy” smoker and in COPD

PLoS ONE

Molecular-phylogenetic characterization of microbial community imbalances in human inflammatory bowel diseases

Proc Natl Acad Sci U S A

Translating Basic Research into Clinical Practice
The Airway Microbiome and Disease