The Fungal Microbiome of the Upper Airway Is Associated With Future Loss of Asthma Control and Exacerbation Among Children With Asthma

Relationship between pediatric asthma and respiratory microbiota, intestinal microbiota: a narrative review

Pediatric asthma is a common chronic airway inflammatory disease that begins in childhood and its impact persists throughout all age stages of patients. With the continuous progress of detection technologies, numerous studies have firmly demonstrated that gut microbiota and respiratory microbiota are closely related to the occurrence and development of asthma, and related research is increasing day by day. This article elaborates in detail on the characteristics, composition of normal gut microbiota and lung microbiota at different ages and in different sites, as well as the connection of the gut-lung axis. Subsequently, it deeply analyzes various factors influencing microbiota colonization, including host factor, delivery mode, maternal dietary and infant feeding patterns, environmental microbial exposure and pollutants, and the use of antibiotics in early life. These factors are highly likely to play a crucial role in the onset process and disease progression of asthma. Research shows that obvious changes have occurred in the respiratory and gut microbiota of asthma patients, and these microbiomes exhibit different characteristics according to the phenotypes and endotypes of asthma. Finally, the article summarizes the microbiota-related treatment approaches for asthma carried out in recent years, including the application of probiotics, nutritional interventions, and fecal microbiota transplantation. These treatment modalities are expected to become new directions for future asthma treatment and bring new hope for solving the problem of childhood asthma.

Allergic Fungal Rhinosinusitis Diagnosis, Management, Associated Conditions, Pathophysiology, and Future Directions: Summary of a Multidisciplinary Workshop

Allergic fungal rhinosinusitis (AFRS) is a unique endotype of chronic rhinosinusitis with nasal polyps (CRSwNP). Despite high recurrence rates and often more severe presenting signs compared with other subtypes of CRSwNP, research dedicated to AFRS has been lacking. Diagnostic criteria are outdated, the mechanistic relationship of AFRS to other associated diseases is unclear, and the pathophysiology of disease and risk factors for recurrence have not been well studied. In December 2023, a multidisciplinary group of rhinologists, otolaryngologists, pulmonologists, allergists, immunologists, scientists, and infectious disease experts met at the National Institute of Health to discuss unmet needs for future AFRS research and care, including patient management, diagnostic criteria, severity, pathophysiology, and related conditions. A summary of these clinical and associated research discussions is included below.

RSV infection in neonatal mice and gastrointestinal microbiome alteration contribute to allergic predisposition

Severe respiratory syncytial virus (RSV) infection during infancy is associated with a 2 to 4-fold increased risk for the development of wheezing and asthma. Recent studies have implicated microbiome changes, either within the lung or gut, during early life can also affect the development of pulmonary disease. Our studies demonstrate long-term gastrointestinal and lung microbiome changes following early life (EL) RSV infection. To determine the respective roles of ELRSV infection and the gut microbiome, we performed germ-free neonatal infection and microbiome colonization using a microbiome from an uninfected animal followed by cockroach allergen (CRA)-induced asthma 4 weeks later. Germ-free animals with ELRSV infection displayed increased airway disease that was diminished by microbiome colonization, including airway hyperreactivity (AHR), mucus, and eosinophil infiltration. To address the role of virus induced gastrointestinal microbiome alterations, we utilized GF mice conventionalized with RSV-associated or naive microbiomes followed by CRA-induced disease. Transfer of neonatal microbiome taken during acute RSV infection did not alter the allergic response to CRA. However, the transfer of a naive adult microbiome conferred protection from enhanced AHR in response to CRA whereas an RSV associated microbiome did not. Taken together, our data indicate that microbiome alteration and early life RSV infection both contribute to allergic predisposition.

Early-Life Host-Microbial Interactions and Asthma Development: A Lifelong Impact?

Childhood is a multifactorial disease, and recent research highlights the influence of early-life microbial communities in shaping disease risk. This review explores the roles of the gut and respiratory microbiota in asthma development, emphasizing the importance of early microbial exposure. The gut microbiota has been particularly well studied, with certain taxa like Faecalibacterium and Bifidobacterium linked to asthma protection, whereas short-chain fatty acids produced by gut microbes support immune tolerance through the gut-lung axis. In contrast, the respiratory microbiota, though low in biomass, shows consistent associations between early bacterial colonization by Streptococcus, Moraxella, and Haemophilus and increased asthma risk. The review also addresses the emerging roles of the skin microbiota and environmental fungi in asthma, though findings remain inconsistent. Timing is a critical factor, with early-life disruptions, such as antibiotic use, potentially leading to increased asthma risk. Despite significant advances, there are still unresolved questions about the long-term consequences of early microbial perturbations, particularly regarding whether microbial dysbiosis is a cause or consequence of asthma. This review integrates current findings, highlighting the need for deeper investigation into cross-organ interactions and early microbial exposures to understand childhood asthma pathophysiology.

The nasal mycobiome of individuals with allergic rhinitis and asthma differs from that of healthy controls in composition, structure and function

Allergic rhinitis (AR) and asthma (AS) are two of the most common chronic respiratory diseases and a major public health concern. Multiple studies have demonstrated the role of the nasal bacteriome in AR and AS, but little is known about the airway mycobiome and its potential association to airway inflammatory diseases. Here we used the internal transcriber spacers (ITS) 1 and 2 and high-throughput sequencing to characterize the nasal mycobiome of 339 individuals with AR, AR with asthma (ARAS), AS and healthy controls (CT). Seven to ten of the 14 most abundant fungal genera (Malassezia, Alternaria, Cladosporium, Penicillium, Wallemia, Rhodotorula, Sporobolomyces, Naganishia, Vishniacozyma, and Filobasidium) in the nasal cavity differed significantly (p ≤ 0.049) between AS, AR or ARAS, and CT. However, none of the same genera varied significantly between the three respiratory disease groups. The nasal mycobiomes of AR and ARAS patients showed the highest intra-group diversity, while CT showed the lowest. Alpha-diversity indices of microbial richness and evenness only varied significantly (p ≤ 0.024) between AR or ARAS and CT, while all disease groups showed significant differences (p ≤ 0.0004) in microbial structure (i.e., beta-diversity indices) when compared to CT samples. Thirty metabolic pathways (PICRUSt2) were differentially abundant (Wald's test) between AR or ARAS and CT patients, but only three of them associated with 5-aminoimidazole ribonucleotide (AIR) biosynthesis were over abundant (log2 Fold Change >0.75) in the ARAS group. AIR has been associated to fungal pathogenesis in plants. Spiec-Easi fungal networks varied among groups, but AR and ARAS showed more similar interactions among their members than with those in the CT mycobiome; this suggests chronic respiratory allergic diseases may disrupt fungal connectivity in the nasal cavity. This study contributes valuable fungal data and results to understand the relationships between the nasal mycobiome and allergy-related conditions. It demonstrates for the first time that the nasal mycobiota varies during health and allergic rhinitis (with and without comorbid asthma) and reveals specific taxa, metabolic pathways and fungal interactions that may relate to chronic airway disease.

Characterization of the oral mycobiome of Portuguese with allergic rhinitis and asthma

Allergic rhinitis and asthma are two prevailing chronic airway diseases and serious public health concerns. Previous research has already described the role of the airway bacteriome in these two diseases, but almost no study so far has explored the mycobiome and its possible association to airway inflammation. Here we sequenced the internal transcribed spacers (ITS) 1 and 2 to characterize the oral mycobiome of 349 Portuguese children and young adults with allergic rhinitis alone (AR) or with asthma (ARAS), asthmatics (AS) and healthy controls (HC). Our genomic analyses showed that the two most abundant fungal phyla (Ascomycota and Basidiomycota) and 3-5 of the 14 most abundant fungal genera (Cladosporium, Aspergillus, Aleurina, Candida and Rhodotorula) in the mouth differed significantly (P ≤ 0.04) between both rhinitic groups and HC. However, none of the same taxa varied significantly between the three respiratory disease groups (AR, ARAS and AS). The oral mycobiomes of respiratory ill patients showed the highest intra-group diversity (microbial richness and evenness), while HC showed the lowest, with all alpha-diversity indices varying significantly (P ≤ 0.0424) between them. Similarly, all disease groups showed significant differences (P ≤ 0.0052) in microbial structure (i.e., beta-diversity indices) when compared to HC samples. Thirty metabolic pathways (PICRUSt2) were differentially abundant (Wald's test) between AR or ARAS and HC patients, but only one of them (D-galactose degradation I) was over abundant (log2 Fold Change >0.75) in the ARAS group. Spiec-Easi fungal networks varied greatly among groups, which suggests chronic respiratory allergic diseases may alter fungal connectivity in the mouth. This study increases our comprehension of the role of the oral mycobiome in allergy-related conditions. It shows for the first time that the oral mycobiota changes during health and allergic rhinitis (with and without asthma comorbidity) and highlights specific taxa, metabolic pathways and fungal interactions that may relate to chronic airway disease.

The Microbiota in Children and Adolescents with Asthma

The role of the respiratory microbiome has been deeply explored for at least two decades. Its characterization using modern methods is now well-defined, and the impacts of many microorganisms on health and diseases have been elucidated. Moreover, the acquired knowledge in related fields enables patient stratification based on their risk for disease onset, and the microbiome can play a role in defining possible phenotypes. The interplay between the lung and gut microbiomes is crucial in determining the microbial composition and immuno-inflammatory reaction. Asthma is still not a well-defined condition, where hyperreactivity and the immune system play important roles. In this disease, the microbiome is mostly represented by Proteobacteria, Streptococcus, and Veillonella, while Cytomegalovirus and Epstein-Barr viruses are the most prevalent viruses. A mycobiome may also be present. The passage from infancy to adolescence is examined by evaluating both the clinical picture and its relationship with possible variations of the microbiome and its effects on asthma. Otherwise, asthma is considered a heterogeneous disease that often starts in childhood and follows a particular personalized track, where adolescence plays a pivotal role in future prognosis. Under this point of view, the microbiota, with its possible variations due to many factors, both internal and external, can modify its composition; consequently, its inflammatory action and role in the immunological response has obvious consequences on the clinical conditions.

The Role of the Microbiome in Pediatric Respiratory Diseases

Numerous studies have examined the role of the microbiome and microbiome-based therapeutics in many childhood airway and lung diseases. In this narrative review, the authors first give a brief overview of the current methods used in microbiome research. The authors then review the literature linking the microbiome with (1) early-life acute respiratory infections due to respiratory syncytial virus, (2) childhood asthma onset, (3) cystic fibrosis, and (4) bronchopulmonary dysplasia, focusing on recent studies that have used culture-independent methods to characterize the respiratory or gut microbiome in the pediatric population.

The airway mycobiome and interactions with immunity in health and chronic lung disease

The existence of commensal fungi that reside within the respiratory tract, termed the airway mycobiome, has only recently been discovered. Studies are beginning to characterize the spectrum of fungi that inhabit the human upper and lower respiratory tract but heterogeneous sampling and analysis techniques have limited the generalizability of findings to date. In this review, we discuss existing studies that have examined the respiratory mycobiota in healthy individuals and in those with inflammatory lung conditions such as asthma, chronic obstructive pulmonary disease and cystic fibrosis. Associations between specific fungi and features of disease pathogenesis are emerging but the precise functional consequences imparted by mycobiota upon the immune system remain poorly understood. It is imperative that further research is conducted in this important area as a more detailed understanding could facilitate the development of novel approaches to manipulating the mycobiome for therapeutic benefit.

Metagenomic insights into fungal community composition of the nasopharyngeal region of COVID-19 associated mucormycosis patients from India

Coronavirus disease 2019 (COVID-19) associated mucormycosis (CAM) was reported predominantly from India during the second wave of COVID-19  and has a high mortality rate. The present study aims to understand the fungal community composition of the nasopharyngeal region of CAM-infected individuals and compare it with severe COVID-19 patients and healthy controls. The fungal community composition was decoded by analyzing the sequence homology of the internal transcribed spacer-2-(ITS-2) region of metagenomic DNA extracted from the upper respiratory samples. The alpha-diversity indices were found to be significantly altered in CAM patients (p < 0.05). Interestingly, a higher abundance of Candida africana, Candida haemuloni, Starmerella floris, and Starmerella lactiscondensi was observed exclusively in CAM patients. The interindividual changes in mycobiome composition were well supported by beta-diversity analysis (p < 0.05). The current study provides insights into the dysbiosis of the nasal mycobiome during CAM infection. In conclusion, our study shows that severe COVID-19 and CAM are associated with alteration in mycobiome as compared to healthy controls. However, the sequential alteration in the fungal flora which ultimately leads to the development of CAM needs to be addressed by future studies.

Can Therapeutic Targeting of the Human Microbiome Influence Asthma Management? A Pro/Con Debate

Asthma is a clinically heterogeneous disease, and despite substantial improvements in therapies, there remains an unmet need for well-tolerated, effective treatments. Observational studies have demonstrated that alterations in the respiratory and gut microbiome are associated with the development of asthma and its severity. These findings are supported by preclinical models demonstrating that respiratory and gut microbes can alter airway inflammation. Therapeutic approaches to target the human microbiome have been increasingly applied to a wide range of acute and chronic diseases, but there are currently no microbiome-based therapeutics approved for the treatment of asthma. This clinical commentary addresses the future role of microbiome-based therapeutics in asthma management from both a pro and con perspective. We examine (1) the prospects for clinical studies demonstrating a causal relationship between the human microbiome and the severity of asthma; (2) the challenges and potential solutions for designing, testing, and implementing a microbiome-based therapeutic; and (3) the possibility of microbiome-based therapeutics for conditions comorbid to asthma. We conclude by identifying research priorities that will help determine the future of microbiome-based therapeutics for the management of asthma.

Lung microbiota and potential treatment of respiratory diseases

The unique microbiome found in the lungs has been studied and shown to be associated with both pulmonary homeostasis and lung diseases. The lung microbiome has the potential to produce metabolites that modulate host-microbe interactions. Specifically, short-chain fatty acids (SCFAs) produced by certain strains of the lung microbiota have been shown to regulate immune function and maintain gut mucosal health. In response, this review described the distribution and composition of the microbiota in lung diseases and discussed the impact of the lung microbiota on health and lung disease. In addition, the review further elaborated on the mechanism of microbial metabolites in microbial-host interaction and their application in the treatment of lung diseases. A better understanding of the interaction between the microbiota, metabolites, and host will provide potential strategies for the development of novel methods for the treatment of pulmonary microbial induced lung diseases.

Respiratory Fungal Communities are Associated with Systemic Inflammation and Predict Survival in Patients with Acute Respiratory Failure

Rationale

Disruption of respiratory bacterial communities predicts poor clinical outcomes in critical illness; however, the role of respiratory fungal communities (mycobiome) is poorly understood.

Objectives

We investigated whether mycobiota variation in the respiratory tract is associated with host-response and clinical outcomes in critically ill patients.

Methods

To characterize the upper and lower respiratory tract mycobiota, we performed rRNA gene sequencing (internal transcribed spacer) of oral swabs and endotracheal aspirates (ETA) from 316 mechanically-ventilated patients. We examined associations of mycobiome profiles (diversity and composition) with clinical variables, host-response biomarkers, and outcomes.

Measurements and Main Results

ETA samples with >50% relative abundance for C. albicans (51%) were associated with elevated plasma IL-8 and pentraxin-3 (p=0.05), longer time-to-liberation from mechanical ventilation (p=0.04) and worse 30-day survival (adjusted hazards ratio (adjHR): 1.96 [1.04-3.81], p=0.05). Using unsupervised clustering, we derived two clusters in ETA samples, with Cluster 2 (39%) showing lower alpha diversity (p<0.001) and higher abundance of C. albicans (p<0.001). Cluster 2 was significantly associated with the prognostically adverse hyperinflammatory subphenotype (odds ratio 2.07 [1.03-4.18], p=0.04) and predicted worse survival (adjHR: 1.81 [1.03-3.19], p=0.03). C. albicans abundance in oral swabs was also associated with the hyperinflammatory subphenotype and mortality.

Conclusions

Variation in respiratory mycobiota was significantly associated with systemic inflammation and clinical outcomes. C. albicans abundance emerged as a negative predictor in both the upper and lower respiratory tract. The lung mycobiome may play an important role in the biological and clinical heterogeneity among critically ill patients and represent a potential therapeutic target for lung injury in critical illness.