Evaluation of Streptococcus mutans strains possessing genes encoding collagen-binding proteins in the Japanese population

Background Streptococcus mutans harbors collagen-binding protein genes, namely cnm and cbm, which are implicated in its virulence and pathogenicity in both oral and extraoral infections. Although both genes were initially identified in S. mutans isolated from Japanese populations, their geographical prevalence, distribution, and genetic relatedness within Japan remain largely unexplored. This study investigates the prevalence of S. mutans strains carrying cnm and cbm genes across Japan, correlates these findings with clinical data, and analyzes the genetic relatedness of cnm-positive and cnm-negative strains using multilocus sequence typing (MLST).
Methods Dental plaque specimens were collected from 1248 individuals from eight Japanese cities (Hiroshima, Fukuoka, Nagasaki, Niigata, Okayama, Osaka, Tokushima, and Tokyo) and plated on selective medium for S. mutans isolation. S. mutans was confirmed in 523 subjects by colony morphology and PCR using species-specific primers, and the presence of the cnm and cbm genes was determined by PCR with gene-specific primers. Demographic (age, sex) and oral examination (caries prevalence, caries experience, number of teeth) data were recorded. MLST was employed to genotype selected cnm-positive and cnm-negative S. mutans strains to assess their clonal relationships.
Results Among 523 subjects possessing S. mutans (aged 3–90 years), we detected cnm-positive strains in all cities; specifically, the prevalence ranged from 5.5% in Okayama to 25.0% in Tokushima. In contrast, cbm-positive strains were less common and undetectable in some regions. Furthermore, subjects harboring cnm-positive S. mutans were significantly older (p = 0.002) and had higher caries prevalence and experience (p < 0.001). MLST revealed evolutionary relationships among cnm-positive strains across the cities but no discernible region-specific clustering. Clonal relationships partially reflected cnm gene distribution, particularly for exclusively cnm-positive or cnm-negative clonal complexes, but inconsistencies involving serotypes and cnm presence within some clonal complexes and sequence types were also noted.
Conclusions The cnm-positive S. mutans strains are widely distributed throughout Japan and are associated with increased age and caries burden. Although core genome analysis revealed some clonal patterns, the non-uniform distribution of the non-core cnm gene is likely influenced by horizontal gene transfer, providing S. mutans with adaptive advantages irrespective of its core genetic background or serotype.