Horizontal Transmission Of Streptococcus Mutans In Caries-active Preschool Children

Dental caries is a common disease endangering children’s oral health,Streptococcus mutans is one of the main pathogenic bacteria causing baby teeth caries.Early colonization of S. mutans in oral cavity of children has important effect on theoccurrence of dental caries. So it is of great significance to research the origins andhorizontal transmission patterns of S. mutans among caries-active preschool children forearly dental caries prevention and control.A large number of studies demonstrated that children’s oral S. mutans not onlyexist in the matriarchal vertical transmission, paternal transmission in the family, thereare horizontal transmissions in close contacts. With the growth of children and theexpansion of their social scope, especially the kindergarten collective life, the horizontaltransmission among close contacts other than the family members became possible.Therefore, the study of horizontal transmission of S. mutans among caries-activepreschool children may provide fundamental supports for prevention of dental caries inchildren.One hundred and eighty-one S. mutans clinical strains were isolated by bacteriamorphology observation, biochemistry and molecular biology identification method indental plaque from20caries-active preschool children aged4-5. Then,37differentgenotypes were identified by AP-PCR, including6children carry1genotype,11children carry2genotypes,2children carry3genotypes,1children carry4genotypes,and we found that two children from different classes carry a kind of the same genotype.We have not found horizontal transmission among these20caries-active preschoolchildren. Finally, the microporous plate culture method was adopted to detect theamount of biofilm forming for10S. mutans strains of different genotypes (S. mutansIngbritt,4different S. mutans genotypes strains from2children with one same genotype, 5highly and poorly cariogenic S. mutans clinical isolated strains identified by ourexperiment group) in seven different periods. We found:(1) The vitro biofilm formingof S. mutans gradually increased from16h. to36h., reached the maximum at36h., anddecreased afterwards;(2) In addition to strain2, the abilities of biofilm forming of theother4strains were in accordance with the highly or poorly cariogenic abilities thatwere identified preciously by our experiment group;(3) Carrying highly cariogenicgenes7and8may be the reason for susceptibility of dental caries in those two children.Gene9which was carried by both of them is not the direct reason for them to becomecaries-active.The present study had not found horizontal transmissions among20caries-activepreschool children, investigated the possible reason for the susceptibility of dentalcaries in two children who carried the same genotype through biofilm formation assay,and analyzed the rule of biofilm forming of S. mutans, which provided the foundationfor further studies on the cariogenic ability of S. mutans. We isolated and identified thecariogenic ability of9S. mutans clinical isolated strains, which offered reliable strainsof different cariogenic abilities for further studies.