Discussion
The difference in β diversity and the distinct differential abundance of certain bacterial taxa in saliva samples from children with moderate to severe asthma who used different inhaled corticosteroid devices (MDI versus DPI) shed light on the potential impact of these devices on the saliva microbiome. Understanding how different inhaler devices affect oral cavity microbiome composition is important, as it may have implications for personalized therapy, choosing optimal devices, and reducing adverse effects in pediatric asthma.
The lack of significant difference in α diversity between MDI and DPI users suggests that overall microbial richness and evenness within individual saliva samples were similar regardless of inhaler device types. However, the β diversity analysis (microbial diversity between samples) revealed significant differences between the MDI and DPI groups. The global diversity-related findings imply that while overall α-diversity within samples may not be affected, specific compositions and taxa of the saliva bacteriome may be associated with the inhaler device type.
Identifying specific bacterial taxa with significant differential abundance between MDI and DPI users provides further insight into the potential impact of inhaler type on saliva and oral bacterial composition. The higher relative abundance of Carnobacteriaceae at the family level and Granulicatella and Aggregatibacter at the genus level in the MDI group suggests that these taxa may be associated with factors unique to MDI usage, such as formulation and administration technique. Granulicatella andAggregatibacter members are among normal oral flora bacteria that may cause serious infections and diseases like infective endocarditis and aggressive periodontitis. 33Aggregatibacter genera, previously known asActinobacillus, 34 is a Gram-negative bacteria from the Pasteurellaceae family and associated with periodontal infection, 35,36 endocarditis, and pneumonia.37 A longitudinal study of 700 adolescents showed the association between aggressive periodontitis and Aggregatibacter actinomycetemcomitans in plaque samples. 38 In addition, a systematic review with meta-analysis reported a significant association between periodontal disease and asthma. 39Granulicatella is from the Carnobacteriaceae family and is a Gram-positive lactic acid bacterium. 33Granulicatella species were shown to be associated with periodontitis, 40 severe childhood caries,41 and endodontic infections. 42,43Understanding the role of these bacterial taxa in oral health, asthma pathogenesis, and their response to corticosteroid inhalation and deposition could provide valuable insights into disease management strategies.
ICS treatment has been reported as a significant contributor to the variability in oral microbiome compositions. Local deposition of ICS may lead to side effects like dysphonia, and oropharyngeal candidiasis, which can be prevented by rinsing the mouth and throat with water after use. 12-15 These side effects add an extra burden to the disease burden on children and their caregivers. Increased doses of ICS intake may result in greater deposition of corticosteroids in the oral cavity and may have a higher impact on oral microbiota composition. Nevertheless, we included the daily doses of ICS intake in our analyses. We have adjusted the analyses, such as global diversity (α and β diversities) and differential abundance analyses (ANCOM-BC) for this confounding factor.
Despite demonstrating lower lung function, children in the DPI group received lower ICS dosages with less frequent intervals and showed a comparable level of asthma control to the MDI group (62%). Additionally, the DPI group exhibited a higher reversibility response to salbutamol, indicating more room for improvement in their lung function. It is important to note that asthma severity should be taken into account, as fewer children in the DPI group had severe asthma (40%) compared to the MDI group (66%). Children with lower lung function may have less respiratory force to inhale and sufficiently transfer corticosteroids into their lungs. So, lower lung function may lead to higher corticosteroid deposition. Which should be taken into account for further research.
This study had multiple strengths. It is the first study to focus on assessing the association between inhaler devices and bacterial microbiome in saliva. It is a multinational European cohort, which increases the generalizability of findings compared to single-center studies. In this study, comprehensive medication intake information, including medications, dosage, intervals, and device type from the last year before inclusion time and/or at the inclusion, was collected by physicians to obtain more accurate data and report more reliable results. In addition, we could assess medication adherence and inhaler techniques and incorporate them into the analyses, which is vital in investigating the association between inhaler devices and saliva microbiome.
There are also limitations related to this study. We do not have information about oral health that can influence the oral microbiome and bacterial composition in saliva. In addition, we have not assessed fungal information from saliva samples; therefore, further research should investigate the link between the salivary fungal and bacterial composition in relation to inhaler device usage. Moreover, even though we assessed medication adherence and inhaler techniques using validated methods, more objective methods like digital inhalers are suggested for future research.
Our findings contribute to a better understanding of the association between inhaler types and oral microbiome and may help optimize personalized treatment in pediatric asthma in the future. The findings indicate that inhaler device types should be recognized as potential confounding factors in asthma microbiome studies. However, more research is needed to further validate the findings and investigate the causal relation between inhaler devices and saliva microbiome.