Distinct composition of the oral indigenous microbiota in South Korean and Japanese adults

Abstract

A comparison of national surveys on oral health suggested that the population of South Korea has a better periodontal health status than that of Japan, despite their similar inherent backgrounds. Here, we investigated differences in oral bacterial assemblages between individuals from those two countries. To exclude potential effects of oral health condition on the microbiota, we selected 52 Korean and 88 Japanese orally healthy adults (aged 40-79 years) from the participants of two cohort studies, the Yangpyeong study in South Korea and the Hisayama study in Japan, and compared the salivary microbiomes. The microbiota of the Japanese individuals comprised a more diverse community, with greater proportions of 17 bacterial genera, including Veillonella, Prevotella, and Fusobacterium, compared to the microbiota of the Korean individuals. Conversely, Neisseria and Haemophilus species were present in much lower proportions in the microbiota of the Japanese individuals than the Korean individuals. Because higher proportions of Prevotella and Veillonella and lower proportions of Neisseria and Haemophilus in the salivary microbiome were implicated in periodontitis, the results of this study suggest that the greater proportion of dysbiotic oral microbiota in the Japanese individuals is associated with their higher susceptibility to periodontitis compared to the Korean individuals.

Figure 1

(A) Principal coordinate analysis (PCoA) plot showing similarity relationships among bacterial community samples from 140 orally healthy individuals (52 South Koreans and 88 Japanese) using the weighted UniFrac distance metric. To correct the unequal number of sequences, we evaluated it based on 1500 randomly selected sequences per sample. The two components explained 48.1 and 16.2% of the variance, respectively. Samples collected in the two countries are depicted using different colors and shapes. (B) Mean number of operational taxonomic unit (OTU), Shannon diversity index and phylogenetic diversity in the salivary microbiota of orally healthy individuals in South Korea (n = 52) and Japan (n = 88). To correct the unequal number of sequences, we evaluated each index of 1500 randomly selected sequences. The significance of differences was evaluated using Student's t-tests. The error bars indicate 95% confidence intervals. (C) Relative abundances of 21 bacterial genera that differed significantly between South Korean and Japanese orally healthy individuals (P < 0.05). The significance of differences was evaluated using Wilcoxon rank-sum test. The error bars indicate 95% confidence intervals.

Figure 2. Relative abundance distribution of operational taxonomic units (OTUs) that were important contributors to differences in the salivary microbiome between orally healthy individuals in Japan and South Korea that were identified using partial least-squares discriminant analysis (PLS-DA).

OTUs with variable importance in projection (VIP) values >2 were selected. The relative abundance of each OTU was normalized to have a mean of 0 and standard deviation of 1 (z-score normalization), and is represented by the color intensity of each grid (blue, low abundance; red, high abundance). The OTUs were ordered according to the results of a hierarchical cluster analysis using correlation distance with average linkage (shown as a dendrogram on the left).