Achievements
Discovery of candidate symbiotic bacteria that regulate oral environment
Hyogo Medical University School of Medicine Department of Oral and Maxillofacial Surgery A research group led by Chief Professor Hiromitsu Kishimoto, Clinical Professor Kazuma Noguchi, Hyogo Medical University Hospital Dental and Oral Surgery Hospital Assistant Shotaro Hanawa, and Hyogo Medical University School of Medicine Department of Microbiology Senior Professor Satoshi Ishido analyzed the salivary bacterial flora of oral cancer patients and healthy subjects, and found that the good bacteria (The genera Rothia and Streptococcus). In addition, we found a strong correlation between the genera Rothia and Streptococcus, revealing that the representative species, Rothia dentocariosa, supports the survival of Streptococcus salivarius. This showed that as a probiotic, simultaneous administration of both bacterial species can be expected to maintain a more stable and healthy oral environment.
This paper was published on September 5, 2025 in "Microbiology spectrum".
Topic
Identification of beneficial symbiont candidates in commensalism as potential oral gatekeepers
Main author
Sotaro Hanawa (Assistant at Dental and Oral Surgery Hospital)
Satoshi Ishido (Professor, Department of Department of Microbiology)
Kazuma Noguchi (Professor of Department of Oral and Maxillofacial Surgery)
Hiromitsu Kishimoto (Professor, Department Department of Oral and Maxillofacial Surgery)
Key points of the research
1. Our university's Department of Oral and Maxillofacial Surgery, pathology, and Department of Microbiology took the lead in working with the RIKEN Institute and Kansai Medical University to identify candidates for so-called beneficial bacteria in the oral cavity.
2. We identified potential beneficial bacteria that help beneficial bacteria.
3. We identified the mechanism of support provided by potential beneficial bacteria.
4. It is believed that by administering the beneficial bacteria discovered in this study as probiotics, it will be possible to maintain a more stable and healthy oral environment.
Research Background
The incidence of oral cancer is currently increasing worldwide. Chronic inflammation, such as periodontitis, is thought to be a cause of cancer development. Furthermore, it has been reported that chronic inflammation is caused by an imbalance in the oral bacterial flora, known as dysbiosis. Therefore, maintaining a healthy oral environment has attracted attention as a means of preventing inflammation and cancer. Currently, administration of so-called beneficial bacteria, such as Streptococcus, is being conducted to maintain the oral environment. However, the effectiveness of these treatments has not been consistently demonstrated. For the beneficial bacteria to be effective, they must colonize the oral cavity, and this establishment depends on the environmental conditions of the existing oral bacterial flora. To further explore the mechanisms of beneficial bacteria and environmental maintenance, we investigated the changes in bacterial communities between oral cancer patients and healthy volunteers, and further examined the changes in bacterial communities between advanced and non-advanced oral cancer. We then attempted to identify candidate beneficial oral bacteria by identifying bacterial communities significantly reduced in cancer and advanced cancer patients. Furthermore, we investigated the interrelationships between these bacteria to investigate the mechanisms of environmental maintenance by the bacterial flora.
Research content and results
The bacterial flora in the saliva of oral cancer patients and healthy volunteers was determined by 16S rRNA sequencing, and the differences and relationships between the bacterial groups were statistically analyzed. Furthermore, bacterial groups that decrease with cancer onset and progression were isolated from the saliva of healthy volunteers, and their interrelationships were analyzed in vitro. As a result, several candidate beneficial bacteria were identified. Among them, a strong correlation was found between the Rothia and Streptococcus genera, and a representative bacterium, Rothia dentocariosa, was found to support the survival of Streptococcus salivarius. Since Streptococcus salivarius is already used clinically to maintain a healthy oral environment, co-administration with Rothia spp. may be able to maintain a more stable and healthy oral environment.
Future challenges
It is necessary to clarify what metabolic products Rothia spp. produce to support Streptococcus spp. It is thought that the use of such metabolic products may promote more stable colonization of Streptococcus spp. in the oral cavity and maintain a healthy environment.
Source of research funds etc.
This research was supported by a JSPS Grant-in-Aid for Scientific Research (Project No. JP23H05357 (Soutaro Hanawa)), a JSPS Grant-in-Aid for Scientific Research (Project No. JP22K09106 (Kyōhei Yoshikawa)), a FY2021 Hyogo Medical University Research Promotion Fund (Kyōhei Yoshikawa), and a FY2021 Hyogo Medical University School of Medicine Graduate Student Support Program (Soutaro Hanawa).