Prevalence and Ecological Role of Streptococcus toyakuensis in Saliva of Healthy Young Individuals.

BACKGROUND AND OBJECTIVES: Antimicrobial resistance (AMR) remains a critical global health concern. In 2022, Streptococcus toyakuensis, a newly identified species with potential multidrug resistance, was isolated from the blood of a patient with sepsis. This study aimed to explore the distribution of S. toyakuensis in the oral microbiome of healthy young individuals and to compare the bacterial community composition between the detection and non-detection groups. METHODS: Sixty saliva samples were randomly collected from 356 healthy young individuals and analyzed using next-generation 16S rRNA sequencing for comprehensive microbial profiling. A taxonomic distribution analysis was performed to compare microbial diversity between S. toyakuensis detection and non-detection groups. Functional analysis identified differentially activated metabolic pathways. RESULTS: S. toyakuensis was detected in 35 of 60 participants. Beta diversity analysis revealed a significant difference in microbial composition between the groups. Linear discriminant analysis effect size showed higher abundance of Neisseria, Haemophilus, Campylobacter, and Capnocytophaga in the detection group, while Actinomyces predominated in the non-detection group. Functional analysis identified 26 significantly different metabolic pathways, including the glyoxylate cycle and L-methionine biosynthesis superpathway. CONCLUSION: The high prevalence of S. toyakuensis in the oral microbiome of healthy young individuals highlights the need for further investigation into its role in AMR dissemination. CLINICAL SIGNIFICANCE: The colonization of S. toyakuensis may influence the oral microbial ecosystem and metabolic activity, potentially facilitating the spread of AMR. Its detection in healthy individuals suggests a silent reservoir, underscoring the importance of oral microbiome surveillance in public health and infection control strategies.