ORAL COLONIZATION BY MORE THAN ONE CLONAL TYPE OF MUTANS STREPTOCOCCUS IN CHILDREN WITH NURSING-BOTTLE DENTAL-CARIES

By ribotyping the genetic diversity of mutans streptococci in six 1.5- 3-yr-old children with nursing-bottle caries and in six caries-free, a ge-matched children and in their mothers was examined. The proportion of mutans streptococci in the dental plaque of the children and their levels in the saliva of the mothers were also examined. For ribotyping , chromosomal DNA of isolates obtained from the plaque of the children (3-12 isolates per child) and from the saliva of the mothers (4-13 is olates per mother) was digested with restriction endonuclease HindIII. The DNA fragments were hybridized to the plasmid pKK3535 which contai ns the rRNA operon of the Escherichia coli chromosome. The results sho wed that children with nursing-bottle caries exposed to frequent consu mption of sucrose had a high proportion of mutans streptococci in plaq ue and four of them were colonized with more than one ribotype, wherea s caries-free children had a low proportion of mutans streptococci in plaque and only one of them harboured more than one ribotype. Mothers of children with nursing bottle caries had similar levels and numbers of ribotypes of mutans streptococci in saliva as the mothers of the ca ries-free children. In both child groups, mothers were probably the ma in source of infection with mutans streptococci. Thus, children with n ursing-bottle caries were not only heavily infected with mutans strept ococci but also often colonized with more than one clonal type. In the child's acquisition of such clones, frequent sugar consumption may ha ve an important role.