Macrolides, inflammation and the lung microbiome: untangling the web of causality

The airway microbiome of persons with cystic fibrosis correlates with acquisition and microbiological outcomes of incident Stenotrophomonas maltophilia infection

Rationale

Chronic infection with Stenotrophomonas maltophilia in persons with cystic fibrosis (pwCF) has been linked to an increased risk of pulmonary exacerbations and lung function decline. We sought to establish whether baseline sputum microbiome associates with risk of S. maltophilia incident infection and persistence in pwCF.

Methods

pwCF experiencing incident S. maltophilia infections attending the Calgary Adult CF Clinic from 2010-2018 were compared with S. maltophilia-negative sex, age (+/-2 years), and birth-cohort-matched controls. Infection outcomes were classified as persistent (when the pathogen was recovered in ≥50% of cultures in the subsequent year) or transient. We assessed microbial communities from prospectively biobanked sputum using V3-V4 16S ribosomal RNA (rRNA) gene sequencing, in the year preceding (Pre) (n = 57), at (At) (n = 22), and after (Post) (n = 31) incident infection. We verified relative abundance data using S. maltophilia-specific qPCR and 16S rRNA-targeted qPCR to assess bioburden. Strains were typed using pulse-field gel electrophoresis.

Results

Twenty-five pwCF with incident S. maltophilia (56% female, median 29 years, median FEV1 61%) with 33 total episodes were compared with 56 uninfected pwCF controls. Demographics and clinical characteristics were similar between cohorts. Among those with incident S. maltophilia infection, sputum communities did not cluster based on infection timeline (Pre, At, Post). Communities differed between the infection cohort and controls (n = 56) based on Shannon Diversity Index (SDI, p = 0.04) and clustered based on Aitchison distance (PERMANOVA, p = 0.01) prior to infection. At the time of incident S. maltophilia isolation, communities did not differ in SDI but clustered based on Aitchison distance (PERMANOVA, p = 0.03) in those that ultimately developed persistent infection versus those that were transient. S. maltophilia abundance within sputum was increased in samples from patients (Pre) relative to controls, measuring both relative (p = 0.004) and absolute (p = 0.001). Furthermore, S. maltophilia abundance was increased in sputum at incident infection in those who ultimately developed persistent infection relative to those with transient infection, measured relatively (p = 0.04) or absolute (p = 0.04), respectively.

Conclusion

Microbial community composition of CF sputum associates with S. maltophilia infection acquisition as well as infection outcome. Our study suggests sputum microbiome may serve as a surrogate for identifying infection risk and persistence risk.

Lung and Gut Microbiome in COPD

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide. The association between lung and gut microbiomes in the pathogenesis of COPD has been recently uncovered. The goal of this study was to discuss the role of the lung and gut microbiomes in COPD pathophysiology. A systematic search of the PubMed database for relevant articles submitted up to June 2022 was performed. We examined the association between the lung and gut microbiome dysbiosis, reflected in bronchoalveolar lavage (BAL), lung tissue, sputum, and feces samples, and the pathogenesis and progression of COPD. It is evident that the lung and gut microbiomes affect each other and both play a vital role in the pathogenesis of COPD. However, more research needs to be carried out to find the exact associations between microbiome diversity and COPD pathophysiology and exacerbation genesis. Another field that research should focus on is the impact of treatment interventions targeting the human microbiome in preventing COPD genesis and progression.

Lung microbial-host interface through the lens of multi-omics

In recent years, our understanding of the microbial world within us has been revolutionized by the use of culture-independent techniques. The use of multi-omic approaches can now not only comprehensively characterize the microbial environment but also evaluate its functional aspects and its relationship with the host immune response. Advances in bioinformatics have enabled high throughput and in-depth analyses of transcripts, proteins and metabolites and enormously expanded our understanding of the role of the human microbiome in different conditions. Such investigations of the lower airways have specific challenges but as the field develops, new approaches will be facilitated. In this review, we focus on how integrative multi-omics can advance our understanding of the microbial environment and its effects on the host immune tone in the lungs.

Targeting the Pulmonary Microbiota to Fight against Respiratory Diseases

The mucosal immune system of the respiratory tract possesses an effective “defense barrier” against the invading pathogenic microorganisms; therefore, the lungs of healthy organisms are considered to be sterile for a long time according to the strong pathogens-eliminating ability. The emergence of next-generation sequencing technology has accelerated the studies about the microbial communities and immune regulating functions of lung microbiota during the past two decades. The acquisition and maturation of respiratory microbiota during childhood are mainly determined by the birth mode, diet structure, environmental exposure and antibiotic usage. However, the formation and development of lung microbiota in early life might affect the occurrence of respiratory diseases throughout the whole life cycle. The interplay and crosstalk between the gut and lung can be realized by the direct exchange of microbial species through the lymph circulation, moreover, the bioactive metabolites produced by the gut microbiota and lung microbiota can be changed via blood circulation. Complicated interactions among the lung microbiota, the respiratory viruses, and the host immune system can regulate the immune homeostasis and affect the inflammatory response in the lung. Probiotics, prebiotics, functional foods and fecal microbiota transplantation can all be used to maintain the microbial homeostasis of intestinal microbiota and lung microbiota. Therefore, various kinds of interventions on manipulating the symbiotic microbiota might be explored as novel effective strategies to prevent and control respiratory diseases.

Nonantimicrobial Actions of Macrolides: Overview and Perspectives for Future Development

Macrolides are among the most widely prescribed broad spectrum antibacterials, particularly for respiratory infections. It is now recognized that these drugs, in particular azithromycin, also exert time-dependent immunomodulatory actions that contribute to their therapeutic benefit in both infectious and other chronic inflammatory diseases. Their increased chronic use in airway inflammation and, more recently, of azithromycin in COVID-19, however, has led to a rise in bacterial resistance. An additional crucial aspect of chronic airway inflammation, such as chronic obstructive pulmonary disease, as well as other inflammatory disorders, is the loss of epithelial barrier protection against pathogens and pollutants. In recent years, azithromycin has been shown with time to enhance the barrier properties of airway epithelial cells, an action that makes an important contribution to its therapeutic efficacy. In this article, we review the background and evidence for various immunomodulatory and time-dependent actions of macrolides on inflammatory processes and on the epithelium and highlight novel nonantibacterial macrolides that are being studied for immunomodulatory and barrier-strengthening properties to circumvent the risk of bacterial resistance that occurs with macrolide antibacterials. We also briefly review the clinical effects of macrolides in respiratory and other inflammatory diseases associated with epithelial injury and propose that the beneficial epithelial effects of nonantibacterial azithromycin derivatives in chronic inflammation, even given prophylactically, are likely to gain increasing attention in the future. SIGNIFICANCE STATEMENT: Based on its immunomodulatory properties and ability to enhance the protective role of the lung epithelium against pathogens, azithromycin has proven superior to other macrolides in treating chronic respiratory inflammation. A nonantibiotic azithromycin derivative is likely to offer prophylactic benefits against inflammation and epithelial damage of differing causes while preserving the use of macrolides as antibiotics.

Integrative microbiomics in bronchiectasis exacerbations

Bronchiectasis, a progressive chronic airway disease, is characterized by microbial colonization and infection. We present an approach to the multi-biome that integrates bacterial, viral and fungal communities in bronchiectasis through weighted similarity network fusion ( https://integrative-microbiomics.ntu.edu.sg ). Patients at greatest risk of exacerbation have less complex microbial co-occurrence networks, reduced diversity and a higher degree of antagonistic interactions in their airway microbiome. Furthermore, longitudinal interactome dynamics reveals microbial antagonism during exacerbation, which resolves following treatment in an otherwise stable multi-biome. Assessment of the Pseudomonas interactome shows that interaction networks, rather than abundance alone, are associated with exacerbation risk, and that incorporation of microbial interaction data improves clinical prediction models. Shotgun metagenomic sequencing of an independent cohort validated the multi-biome interactions detected in targeted analysis and confirmed the association with exacerbation. Integrative microbiomics captures microbial interactions to determine exacerbation risk, which cannot be appreciated by the study of a single microbial group. Antibiotic strategies probably target the interaction networks rather than individual microbes, providing a fresh approach to the understanding of respiratory infection.

Azithromycin and the microbiota of cystic fibrosis sputum

Background

Azithromycin is commonly prescribed drug for individuals with cystic fibrosis (CF), with demonstrated benefits in reducing lung function decline, exacerbation occurrence and improving nutrition. As azithromycin has antimicrobial activity against components of the uncultured microbiome and increasingly the CF microbiome is implicated in disease pathogenesis – we postulated azithromycin may act through its manipulation. Herein we sought to determine if the CF microbiome changed following azithromycin use and if clinical benefit observed during azithromycin use associated with baseline community structure.

Results

Drawing from a prospectively collected biobank we identified patients with sputum samples prior to, during and after initiating azithromycin and determined the composition of the CF microbial community by sequencing the V3-V4 region of the 16S rRNA gene. We categorized patients as responders if their rate of lung function decline improved after azithromycin initiation. Thirty-eight adults comprised our cohort, nine who had not utilized azithromycin in at least 3 years, and 29 who were completely naïve. We did not observe a major impact in the microbial community structure of CF sputum in the 2 years following azithromycin usage in either alpha or beta-diversity metrics. Seventeen patients (45%) were classified as Responders – demonstrating reduced lung function decline after azithromycin. Responders who were naïve to azithromycin had a modest clustering effect distinguishing them from those who were non-Responders, and had communities enriched with several organisms including Stenotrophomonas, but not Pseudomonas.

Conclusions

Azithromycin treatment did not associate with subsequent large changes in the CF microbiome structure. However, we found that baseline community structure associated with subsequent azithromycin response in CF adults.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02159-5.

Treatment of infections in cancer patients: an update from the neutropenia, infection and myelosuppression study group of the Multinational Association for Supportive Care in Cancer (MASCC)

INTRODUCTION

Patients with hematological and advanced solid malignancies have acquired immune dysfunction, often exacerbated by treatment, posing a significant risk for the development of infections. This review evaluates the utility of current clinical and treatment guidelines, in the setting of management of infections in cancer patients.

AREAS COVERED

These include causes of infection in cancer patients, management of patients with high-risk and low-risk febrile neutropenia, management of low-risk patients in an outpatient setting, the role of granulocyte colony-stimulating factor (G-CSF) in the prevention and treatment of neutropenia-related infections, management of lung infections in various clinical settings, and emerging challenges surrounding the risk of infection in cancer patients treated with novel treatments. The literature search was performed by accessing PubMed and other databases, focusing on published clinical trials of relevant anti-cancer agents and diseases, primarily covering the recent past, but also including several key studies published during the last decade and, somewhat earlier in a few cases.

EXPERT REVIEW

Notwithstanding the promise of gene therapy/gene editing in hematological malignancies and some types of solid cancers, innovations introduced in clinical practice include more discerning clinical management such as the generalized use of biosimilar formulations of G-CSF and the implementation of novel, innovative immunotherapies.

Lower Airway Dysbiosis Affects Lung Cancer Progression

In lung cancer, enrichment of the lower airway microbiota with oral commensals commonly occurs, and ex vivo models support that some of these bacteria can trigger host transcriptomic signatures associated with carcinogenesis. Here, we show that this lower airway dysbiotic signature was more prevalent in the stage IIIB-IV tumor-node-metastasis lung cancer group and is associated with poor prognosis, as shown by decreased survival among subjects with early-stage disease (I-IIIA) and worse tumor progression as measured by RECIST scores among subjects with stage IIIB-IV disease. In addition, this lower airway microbiota signature was associated with upregulation of the IL17, PI3K, MAPK, and ERK pathways in airway transcriptome, and we identified Veillonella parvula as the most abundant taxon driving this association. In a KP lung cancer model, lower airway dysbiosis with V. parvula led to decreased survival, increased tumor burden, IL17 inflammatory phenotype, and activation of checkpoint inhibitor markers. SIGNIFICANCE: Multiple lines of investigation have shown that the gut microbiota affects host immune response to immunotherapy in cancer. Here, we support that the local airway microbiota modulates the host immune tone in lung cancer, affecting tumor progression and prognosis.See related commentary by Zitvogel and Kroemer, p. 224.This article is highlighted in the In This Issue feature, p. 211.

Risk factors associated with COVID-19-associated pulmonary aspergillosis in ICU patients: a French multicentric retrospective cohort

OBJECTIVES

The main objective of this study was to determine the incidence of invasive pulmonary aspergillosis (IPA) in patients with coronavirus disease 2019 (COVID-19) admitted to the intensive care unit (ICU), and to describe the patient characteristics associated with IPA occurrence and to evaluate its impact on prognosis.

METHODS

We conducted a retrospective cohort study including all successive COVID-19 patients, hospitalized in four ICUs, with secondary deterioration and one or more respiratory samples sent to the mycology department. We used a strengthened IPA testing strategy including seven mycological criteria. Patients were classified as probable IPA according to the European Organization for Research and Treatment of Cancer (EORTC)/Mycoses Study Group Education and Research Consortium (MSGERC) classification if immunocompromised, and according to the recent COVID-19-associated IPA classification otherwise.

RESULTS

Probable IPA was diagnosed in 21 out of the 366 COVID-19 patients (5.7%) admitted to the ICU and in the 108 patients (19.4%) who underwent respiratory sampling for deterioration. No significant differences were observed between patients with and without IPA regarding age, gender, medical history and severity on admission and during hospitalization. Treatment with azithromycin for ≥3 days was associated with the diagnosis of probable IPA (odds ratio 3.1, 95% confidence interval 1.1-8.5, p = 0.02). A trend was observed with high-dose dexamethasone and the occurrence of IPA. Overall mortality was higher in the IPA patients (15/21, 71.4% versus 32/87, 36.8%, p < 0.01).

CONCLUSION

IPA is a relatively frequent complication in severe COVID-19 patients and is responsible for increased mortality. Azithromycin, known to have immunomodulatory properties, may contribute to increase COVID-19 patient's susceptibility to IPA.

Low-dose and long-term azithromycin significantly decreases Staphylococcus aureus in the microbiome of refractory CRS patients

BACKGROUND

The sinonasal microbiome is believed to play an important role in the pathophysiology of refractory chronic rhinosinusitis (CRS). We evaluated changes in the microbiome following a 4-month course of low-dose azithromycin. Assessing microbiome alterations following such a treatment may help identify underlying mechanisms of this drug.

METHODS

A total of 48 adults with refractory CRS were enrolled in a double-blind, randomized, placebo-controlled trial. Patients were randomized to 250 mg of azithromycin or placebo 3 times weekly for 4 months. During this time, daily budesonide saline irrigations were continued. Sinonasal swabs were collected by endoscopically-assisted method prior to treatment initiation and at the end of it, and sent for 16S ribosomal RNA gene sequencing. High-resolution ANCHOR pipeline was used to infer and annotate putative species. The 2 patient groups were compared using DESeq2 differential abundance analysis.

RESULTS

From initiation to the end of azithromycin treatment, patients showed a significant difference in beta diversity analysis (p = 0.0004) along with a significant decrease in 71 different operational taxonomic units (OTUs) of Staphylococcus aureus (false discovery rate [FDR] < 0.05) obtained from the differential abundance analysis. This was not observed in placebo-treated patients. By the end of treatments, azithromycin-treated patients had a significant decrease in 29 different OTUs of S. aureus (FDR < 0.05) when compared to placebo.

CONCLUSION

A 4-month course of 250 mg of azithromycin 3 times weekly in patients with refractory CRS significantly decreases S. aureus abundance in the sinonasal microbiome. Considering the pathogenic role of S. aureus in the refractory CRS population, azithromycin may constitute an additional therapeutic option to help control this disease.

Bronchiectasis in rheumatoid arthritis. A clinical appraisial

Bronchiectasis is defined as irreversibly damaged and dilated bronchi and is one of the most common pulmonary manifestations in patients with rheumatoid arthritis (RA). The model of RA-associated autoimmunity induced in some individuals by chronic bacterial infection in bronchiectasis is becoming increasingly acceptable, although a genetic predisposition to RA-associated bronchiectasis has also been demonstrated. Bronchiectasis should be suspected in RA patients with chronic cough and sputum production or frequent respiratory infections and the diagnosis must be confirmed by thoracic high-resolution computed tomography. Management of patients with RA-associated bronchiectasis includes a multimodal treatment approach. Similar to all patients with non-cystic fibrosis bronchiectasis, patients with RA-associated bronchiectasis benefit from a pulmonary rehabilitation program, including an exercise/muscle strengthening program and an education program with a specific session on airway clearance techniques. Prophylactic antibiotics are recommended for patients with frequent (3 or more infective exacerbations per year) or severe infections requiring hospitalization/intravenous antibiotics and inhaled corticosteroids and long-acting β2-agonists should be used in patients with non-cystic fibrosis bronchiectasis and associated airway hyper-responsiveness. In patients with RA-associated bronchiectasis the use of immunomodulatory drugs has to be carefully considered, as they are essential to control disease activity, despite being associated with an increased infectious risk. Pneumococcal and influenza vaccines are advised to all patients with RA-associated bronchiectasis in order to reduce the risk of infection. Patients with RA-associated bronchiectasis have a poorer prognosis than those with either RA or bronchiectasis alone and require regular follow-up, under the joint care of a rheumatologist and a pulmonologist.

The pulmonary microbiome: challenges of a new paradigm

The study of the human microbiome-and, more recently, that of the respiratory system-by means of sophisticated molecular biology techniques, has revealed the immense diversity of microbial colonization in humans, in human health, and in various diseases. Apparently, contrary to what has been believed, there can be nonpathogenic colonization of the lungs by microorganisms such as bacteria, fungi, and viruses. Although this physiological lung microbiome presents low colony density, it presents high diversity. However, some pathological conditions lead to a loss of that diversity, with increasing concentrations of some bacterial genera, to the detriment of others. Although we possess qualitative knowledge of the bacteria present in the lungs in different states of health or disease, that knowledge has advanced to an understanding of the interaction of this microbiota with the local and systemic immune systems, through which it modulates the immune response. Given this intrinsic relationship between the microbiota and the lungs, studies have put forth new concepts about the pathophysiological mechanisms of homeostasis in the respiratory system and the potential dysbiosis in some diseases, such as cystic fibrosis, COPD, asthma, and interstitial lung disease. This departure from the paradigm regarding knowledge of the lung microbiota has made it imperative to improve understanding of the role of the microbiome, in order to identify possible therapeutic targets and to develop innovative clinical approaches. Through this new leap of knowledge, the results of preliminary studies could translate to benefits for our patients.

Microbiota in Exhaled Breath Condensate and the Lung

The lung microbiota is commonly sampled using relatively invasive bronchoscopic procedures. Exhaled breath condensate (EBC) collection potentially offers a less invasive alternative for lung microbiota sampling. We compared lung microbiota samples retrieved by protected specimen brushings (PSB) and exhaled breath condensate collection. We also sought to assess whether aerosolized antibiotic treatment would influence the lung microbiota and whether this change could be detected in EBC. EBC was collected from 6 conscious sheep and then from the same anesthetized sheep during mechanical ventilation. Following the latter EBC collection, PSB samples were collected from separate sites within each sheep lung. On the subsequent day, each sheep was then treated with nebulized colistimethate sodium. Two days after nebulization, EBC and PSB samples were again collected. Bacterial DNA was quantified using 16S rRNA gene quantitative PCR. The V2-V3 region of the 16S rRNA gene was amplified by PCR and sequenced using Illumina MiSeq. Quality control and operational taxonomic unit (OTU) clustering were performed with mothur. The EBC samples contained significantly less bacterial DNA than the PSB samples. The EBC samples from anesthetized animals clustered separately by their bacterial community compositions in comparison to the PSB samples, and 37 bacterial OTUs were identified as differentially abundant between the two sample types. Despite only low concentrations of colistin being detected in bronchoalveolar lavage fluid, PSB samples were found to differ by their bacterial compositions before and after colistimethate sodium treatment. Our findings indicate that microbiota in EBC samples and PSB samples are not equivalent.

IMPORTANCE Sampling of the lung microbiota usually necessitates performing bronchoscopic procedures that involve a hospital visit for human participants and the use of trained staff. The inconvenience and perceived discomfort of participating in this kind of research may deter healthy volunteers and may not be a safe option for patients with advanced lung disease. This study set out to evaluate a less invasive method for collecting lung microbiota samples by comparing samples taken via protected specimen brushings (PSB) to those taken via exhaled breath condensate (EBC) collection. We found that there was less bacterial DNA in EBC samples compared with that in PSB samples and that there were differences between the bacterial communities in the two sample types. We conclude that while EBC and PSB samples do not produce equivalent microbiota samples, the study of the EBC microbiota may still be of interest.