Salivary Oral Microbiome of Children With Juvenile Idiopathic Arthritis: A Norwegian Cross-Sectional Study

Abstract

Background: The oral microbiota has been connected to the pathogenesis of rheumatoid arthritis through activation of mucosal immunity. The objective of this study was to characterize the salivary oral microbiome associated with juvenile idiopathic arthritis (JIA), and correlate it with the disease activity including gingival inflammation.

Methods: Fifty-nine patients with JIA (mean age, 12.6 ± 2.7 years) and 34 healthy controls (HC; mean age 12.3 ± 3.0 years) were consecutively recruited in this Norwegian cross-sectional study. Information about demographics, disease activity, medication history, frequency of tooth brushing and a modified version of the gingival bleeding index (GBI) and the simplified oral hygiene index (OHI-S) was obtained. Microbiome profiling of saliva samples was performed by sequencing of the V1-V3 region of the 16S rRNA gene, coupled with a species-level taxonomy assignment algorithm; QIIME, LEfSe and R-package for Spearman correlation matrix were used for downstream analysis.

Results: There were no significant differences between JIA and HC in alpha- and beta-diversity. However, differential abundance analysis revealed several taxa to be associated with JIA: TM7-G1, Solobacterium and Mogibacterium at the genus level; and Leptotrichia oral taxon 417, TM7-G1 oral taxon 352 and Capnocytophaga oral taxon 864 among others, at the species level. Haemophilus species, Leptotrichia oral taxon 223, and Bacillus subtilis, were associated with healthy controls. Gemella morbillorum, Leptotrichia sp. oral taxon 498 and Alloprevotella oral taxon 914 correlated positively with the composite juvenile arthritis 10-joint disease activity score (JADAS10), while Campylobacter oral taxon 44 among others, correlated with the number of active joints. Of all microbial markers identified, only Bacillus subtilis and Campylobacter oral taxon 44 maintained false discovery rate (FDR) < 0.1.

Conclusions: In this exploratory study of salivary oral microbiome we found similar alpha- and beta-diversity among children with JIA and healthy. Several taxa associated with chronic inflammation were found to be associated with JIA and disease activity, which warrants further investigation.

Keywords: 16S rRNA; juvenile idiopathic arthritis; next generation sequencing (NGS); oral health; salivary microbiome.

Figure 1

Microbiological profiles. DNA extracted from saliva was sequenced for the V1-V3 region of the 16S rRNA gene using paired-end chemistry. The generated reads were merged, quality-filtered and classified to the species level using a BLASTn-based algorithm. The stacked bars show the average relative abundances of all phyla and top genera and species (those with relative abundance ≥ 1%) identified in the study groups. OT, oral taxon.

Figure 2

Species richness and diversity. Taxonomic profiles were rarified and used to calculate observed richness, expected richness (alpha diversity index; Chao index), evenness measure (alpha diversity index; Shannon’s and Simpson’s) and distance matrices employing standard QIIME scripts. Left: Box and whisker plots of species richness and aloha diversity in each group. Differences were not significant by Mann–Whitney U test. Right: Clustering of samples with PCoA based on abundance Jaccard distance matrix. Plots were generated with QIIME and R Package.

Figure 3

Differentially abundant taxa. (A) Phyla, (B) Genera and (C) species that showed significant differences in relative abundance between the two study groups as identified by linear discriminant analysis (LDA) effect size analysis (LEfSe) – 2.5 LDA score cutoff. OT, oral taxon. **FDR ≤ 0.1 (Benjamini-Hochberg method).

Figure 4

Per sample abundance plots. Relative abundances of top six differentially abundant species (based on LDA score) in individual samples. OT, oral taxon. FDR ≤ 0.1 (Benjamini-Hochberg method).

Figure 5

Heatmap of the microbial association with disease activity. A Spearman correlation matrix was computed using R package. Correlations with P-value ≤ 0.01 were considered significant. The r-value for nonsignificant correlations was set to zero (blue on the heatmap). OT, oral taxon. **FDR ≤ 0.1 (Benjamini-Hochberg method). PRgloVAS; patient reported global assessment of well-being; ESR, erythrocyte sedimentation rate; JADAS10, the composite juvenile idiopathic arthritis 10-joint disease activity score; MDgloVAS, the medical doctor global evaluation of disease activity.

Figure 6

Differentially abundant taxa by TMJ arthritis. (A) Phyla, (B) Genera and (C) species that showed significant differences in relative abundance between the JIA subjects with and without TMJ involvement, as identified by linear discriminant analysis (LDA) effect size analysis (LEfSe). 2.5 LDA score cutoff. OT, oral taxon. **FDR ≤ 0.1 (Benjamini-Hochberg method).