Population genetic studies can contribute to current knowledge about the epidemiology of pathogens such as Streptococcus mutans, which is one of the most widely distributed bacteria in the world to be associated with human dental caries. In the present study, we investigated whether the population genetic structure of the species is clonal or recombinant, and we also evaluated the current levels of gene flow, admixed ancestry, and the hypothesis of an expansion of the bacteria within the last 10 000 years. Strains of S. mutans from C ordoba (Argentina) were obtained, with sequences of the genes aroE, gltA, gyrA, and lepC genes being aligned with those of strains from Japan, Thailand, and Finland. Most of our statistical analyses performed on the DNA matrix of 193 strains supported the existence of recombination at the intergene level. We also estimated the number of genetic clusters via Bayesian analyses, with three genetic clusters being detected in the four countries at different frequencies, as well as the number of strains with pure or admixed ancestry varying among countries. Argentina revealed 50% admixed strains, whereas these types of strains were present in only 8-19% of the other three countries analyzed. This result could be associated with the important human migration waves that Argentina has experienced, which may have mixed strains of S. mutans of different geographical origins. The demographic history was obtained using Extended Bayesian Skyline Plot anslysis, which showed important growth in the effective population size approximately 5000 years ago, coincident with the beginning of the dispersion of agriculture and a change to a diet rich in carbohydrates.

BackgroundCaries is a worldwide distributed oral disease of multifactorial nature, with Streptococcus mutans being the most commonly isolated bacterial agent. The glycosyltransferases of this bacterium would play an essential role in the aetiology and pathogenesis of caries.AimWe explored how the glucosyltransferase‐B (gtf‐B) gene variability of S. mutans from children in central Argentina correlated with their caries experience and how these strains were genetically related to those of other countries.DesignDental examinations were performed on 59 children; dmft and DMFT indexes were calculated. From stimulated saliva, S. mutans was grown and counted (CFU/mL). From bacterial DNA, the gtf‐B gene was amplified and sequenced. Alleles were identified and their genealogical relationships established. Clinical, microbiological, and genetic variables were correlated with caries experience. Our sequences were included in a matrix with those from 16 countries (n = 358); genealogical relationships among alleles were obtained. Population genetic analyses were performed for countries with >20 sequences.ResultsThe mean dmft + DMFT was 6.45. Twenty‐two gtf‐B alleles were identified here, which showed low genetic differentiation in the network. Caries experience was correlated with CFU/mL, but not with allele variation. Low differentiation was found among the 70 alleles recovered from the 358 sequences and among the countries analyzed.ConclusionIn this study, caries experience in children was correlated with the number of CFU/mL of S. mutans but not with the gtf‐B gene variability. Combined genetic analyses of worldwide strains support the theory that this bacterium experienced population expansions, probably associated with agriculture development and/or food industrialization.