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.