Streptococcus mutans is the major pathogen of dental caries, a biofilm-dependent infectious disease, and occasionally causes infective endocarditis. S. mutans strains have been classified into four serotypes (c, e, f, and k). However, little is known about the S. mutans population, including the clonal relationships among strains of S. mutans, in relation to the particular clones that cause systemic diseases. To address this issue, we have developed a multilocus sequence typing (MLST) scheme for S. mutans. Eight housekeeping gene fragments were sequenced from each of 102 S. mutans isolates collected from the four serotypes in Japan and Finland. Between 14 and 23 alleles per locus were identified, allowing us theoretically to distinguish more than 1.2 ؋ 10 10 sequence types. We identified 92 sequence types in these 102 isolates, indicating that S. mutans contains a diverse population. Whereas serotype c strains were widely distributed in the dendrogram, serotype e, f, and k strains were differentiated into clonal complexes. Therefore, we conclude that the ancestral strain of S. mutans was serotype c. No geographic specificity was identified. However, the distribution of the collagen-binding protein gene (cnm) and direct evidence of mother-to-child transmission were clearly evident. In conclusion, the superior discriminatory capacity of this MLST scheme for S. mutans may have important practical implications.Streptococcus mutans is the major pathogen of dental caries, a biofilm-dependent infectious disease. These organisms prevail in the complex microcommunity of the oral biofilm in the presence of sucrose, under the extremely low pHs responsible for tooth demineralization. This organism is also a possible causative agent of infective endocarditis (9). S. mutans has been classified into four serotypes (c, e, f, and k) based on the chemical composition of its cell surface rhamnose-glucose polymers. The genes involved in the synthesis of serotypespecific polymers have been cloned and sequenced. Four rml genes (rmlA-rmlD) are related to the synthesis of dTDP-Lrhamnose (37, 38), and gluA is involved in the production of the immediate precursor of the glucose side chain (42). The six-gene operon (rgpA-rgpF) and rgpG, which are required for the synthesis of rhamnose-glucose polymers, have also been cloned and sequenced (41, 43). Serotype-specific genes just downstream from the rgpA-rgpF operon have also been sequenced, and this region is highly diverse among these serotypes (33). Therefore, the strains of each serotype of S. mutans are thought to have evolved and spread independently.In a previous study, we showed that some blood isolates of S. mutans that cannot be classified into the c, e, or f serotype have negligible amounts of glucose side chains, despite the presence of the rhamnose backbone in serotype-specific polysaccharides (21). We designated the novel serotype as serotype "k" and showed that serotype k strains are less susceptible to phagocytosis by human polymorphonuclear leukocytes. Most oral isolates are ...

A new reliable genotyping method, multilocus sequence typing (MLST), was used to evaluate vertical transmission of the cariogenic pathogen Streptococcus mutans. A total of 136 S. mutans strains were isolated from saliva samples of 20 Japanese mother-child pairs, including 5 girls and 5 boys with primary dentition, and 5 girls and 5 boys with mixed dentition. The nucleotide sequences of 8 partial housekeeping genes, aroE, murI, gltA, glnA, glk, tkt, lepC, and gyrA, were analyzed and a similarity for all of those sequences between strains from a mother-child pair was regarded as indicating transmission, which was shown in 70% of the pairs. Interestingly, the rate of transmitted strains from mothers was significantly higher in the girls (90%) than in the boys (p = 0.001). Furthermore, the S. mutans sequence type (ST) with the highest distribution percentage in each maternal saliva sample was found to be transferred to their children. In addition, variations in two large conjugative-transfer associated regions, TnSmu1 and TnSmu2, were determined and compared with the STs defined by MLST. No variations in those two regions shown by PCR patterns were present in any of the strains isolated from the same families with the same STs, though isolates of some STs from different families showed distinct patterns for TnSmu2. Our results indicate that mothers are the main source for transmission of S. mutans to their children, while the present MLST method was also shown to be useful for investigating bacterial transmission.