**Yoshiaki Nomura 1,\*, Erika Kakuta 2, Noboru Kaneko 3, Kaname Nohno 3, Akihiro Yoshihara <sup>4</sup> and Nobuhiro Hanada <sup>1</sup>**


Received: 19 August 2020; Accepted: 15 September 2020; Published: 16 September 2020

**Abstract:** For a healthy oral cavity, maintaining a healthy microbiome is essential. However, data on healthy microbiomes are not sufficient. To determine the nature of the core microbiome, the oral-microbiome structure was analyzed using pyrosequencing data. Saliva samples were obtained from healthy 90-year-old participants who attended the 20-year follow-up Niigata cohort study. A total of 85 people participated in the health checkups. The study population consisted of 40 male and 45 female participants. Stimulated saliva samples were obtained by chewing paraffin wax for 5 min. The V3–V4 hypervariable regions of the 16S ribosomal RNA (rRNA) gene were amplified by PCR. Pyrosequencing was performed using MiSeq. Operational taxonomic units (OTUs) were assigned on the basis of a 97% identity search in the EzTaxon-e database. Using the threshold of 100% detection on the species level, 13 species were detected: *Streptococcus sinensis*, *Streptococcus pneumoniae*, *Streptococcus salivarius*, KV831974\_s, *Streptococcus parasanguinis*, *Veillonella dispar*, *Granulicatella adiacens*, *Streptococcus*\_uc, *Streptococcus peroris*, KE952139\_s, *Veillonella parvula*, *Atopobium parvulum*, and AFQU\_vs. These species represent potential candidates for the core make-up of the human microbiome.

**Keywords:** oral microbiome; pyrosequencing; core microbiome; elderly
