The human oral microbiome comprises multi-kingdom microbes including bacteria, archaea, eukaryotes, and viruses, which play major roles in assisting oral health and overall health [1]. The oral microbiome influences human health via its translocation, its metabolites, the elements circulating in the bloodstream, and so on [[2], [3], [4], [5]]. Thus, the dysbiosis of oral microbiome is associated with many oral diseases including dental caries, periodontal disease, and oral cancer, as well as associated with some systemic diseases including Alzheimer’s disease, diabetes, cardiovascular disease, colorectal cancer, inflammatory bowel disease, rheumatoid arthritis, and obesity [1].

Microbiome signature, rather than single microorganism, has been found to be an indicator of human health [6]. Moreover, enterotypes are proposed to summarize the human gut microbial characteristics among different populations, which are defined based on the bacterial or fungal compositional patterns and show significant efficacy in stratifying populations from health and disease [7,8]. As a niche second only to the gut in microbial diversity, the oral cavity harbors more than 700 bacterial species and more than 100 fungal genera [1]. Although the oral cavity is directly connected to the gut and the oral microorganisms can translocate to the gut, these two niches are physiologically distinct [9]. Moreover, due to the differences of environment and function, there are significant differences in the composition of the microbiota between the oral cavity and the intestinal tract [10]. Thus, it is necessary to depict the microbial characteristics of the oral cavity. The oral microbiota in different populations has been revealed, such as patients with periodontitis [11], head and neck squamous cell carcinoma (HNSCC) [12], hypertension [13], Alzheimer's disease [14], etc. However, whether enterotype-like characteristics also exist in the human oral cavity is still unclear.

Thus, this study aimed to depict the characteristics of the oral microbiome in human populations. Considering that the clusters identified in gut microbiome were previously named as “enterotypes” [7], the identified clusters in oral microbiome were termed “oraltypes”.