Tongue Coating and Salivary Microbiome Analysis in Children With Halitosis

Objectives: To better characterise differences in the tongue coating and saliva microbial communities of healthy children and children with halitosis.
Methods: This study protocol was approved by the Ethics Committee of Peking University School and Hospital of Stomatology (PKUSSIRB-2012062). Tongue coating and saliva samples were collected from ten healthy subjects and 10 subjects with halitosis. Samples were processed by 454 pyrosequencing of the 16S rRNA gene V1-V3 hypervariable region, followed by bioinformatic analyses.
Results: The halitosis tongue coatings showed greater α diversity than healthy ones. Leptotrichia wadei (OTU 398) and Peptostreptococcus stomatis (OTU 135) were detected in higher proportions (relative abundance) and frequency (prevalence) in halitosis tongue coatings compared to healthy samples, while Prevotella shahii (OTU 283) was more abundant and prevalent in halitosis-affected saliva. Co-abundance analyses revealed that tongue coatings, compared to saliva, tended to harbour distinct halitosis-associated bacteria, while the co-occurrence network and α diversity analyses revealed saliva with a more stable character, indicating that the tongue coating and saliva microbiomes followed different mechanisms leading to halitosis. We also defined the "core microbiome" in tongue coatings.
Conclusions: We identified several species that differed significantly in relative abundance and frequency of detection, providing a list of candidate halitosis-associated pathogens. However, the aetiology of halitosis is multi-microbial and more complex than we expected, and further experiments are required to gain a better understanding of the condition.