Salivary Microbiome Diversity in Caries-Free and Caries-Affected Children

Abstract

Dental caries (tooth decay) is an infectious disease. Its etiology is not fully understood from the microbiological perspective. This study characterizes the diversity of microbial flora in the saliva of children with and without dental caries. Children (3-4 years old) with caries (n = 20) and without caries (n = 20) were recruited. Unstimulated saliva (2 mL) was collected from each child and the total microbial genomic DNA was extracted. DNA amplicons of the V3-V4 hypervariable region of the bacterial 16S rRNA gene were generated and subjected to Illumina Miseq sequencing. A total of 17 phyla, 26 classes, 40 orders, 80 families, 151 genera, and 310 bacterial species were represented in the saliva samples. There was no significant difference in the microbiome diversity between caries-affected and caries-free children (p > 0.05). The relative abundance of several species (Rothia dentocariosa, Actinomyces graevenitzii, Veillonella sp. oral taxon 780, Prevotella salivae, and Streptococcus mutans) was higher in the caries-affected group than in the caries-free group (p < 0.05). Fusobacterium periodonticum and Leptotrichia sp. oral clone FP036 were more abundant in caries-free children than in caries-affected children (p < 0.05). The salivary microbiome profiles of caries-free and caries-affected children were similar. Salivary counts of certain bacteria such as R. dentocariosa and F. periodonticum may be useful for screening/assessing children's risk of developing caries.

Keywords: 16S rRNA gene; children; early childhood caries; etiology; microbiome; saliva.

Figure 1

Phylogenetic diversity (mean ± SD) of the salivary microbiomes of the caries-affected (CA) and caries-free (CF) children.

Figure 2

Rarefaction curves for the caries-affected (CA) and caries-free (CF) children.

Figure 3

Comparison of community structures within and between the caries-affected (CA) and caries-free (CF) groups. (A) Heatmap of the weighted UniFrac distance within and across the CA and CF groups; (B) The weighted UniFrace distance values (mean ± SD) of the CA and CF groups.

Figure 4

Curves of shared and unshared OTUs (mean ± SD) among children in the caries-affected (CA) and caries-free (CF) groups. (A) Unshared OTUs among children in the CA and CF groups; (B) Shared OTUs among children in the CA and CF groups.

Figure 5

Venn diagram of the number of OTUs shared and unshared in the caries-affected (CA) and caries-free (CF) groups.

Figure 6

Analyses of the predominant bacterial genera in the caries-affected (CA) and caries-free (CF) groups.

Figure 7

Comparison of the bacterial composition between the caries-affected (CA) and caries-free (CF) groups at the species level. (A) The predominant species in both CA and CF groups; (B) Bacterial species significantly more prevalent in the CA or CF groups (* p < 0.05).