Demonstration of identical strains of mutans streptococci within Chinese families by genotyping.

The aim of this study was to investigate the intra-familial distribution of mutans streptococci in some Chinese families. Eighteen families consisting of mother, father and a 3-yr-old child without any older siblings participated. Clinical examination and interview were performed to obtain information about level of mutans streptococci in saliva, caries prevalence scored by DMFT or deft, general health, diet regimens, breast-feeding time, principal caretaker of the child and the parents' profession. At the same appointment, two pooled plaque samples from each subject were collected with the tips of sterile tooth picks. From these plaque samples, mutans streptococci were isolated on MSB-agar plates and identified by serotyping. Pure isolates were obtained from all subjects of 11 families. These isolates were genotyped using restriction endonuclease HaeIII. The results showed that in 4 families the mothers shared genotype with the child, and in 3 families it was the father and the child who harboured a similar genotype. In 2 families, all subjects harboured an identical genotype. Further, the spouses in one parental pair showed an identical genotype, and, finally, in one family all subjects harboured their unique genotypes. None of the investigated factors could explain the differences in the intra-familial distribution of mutans streptococci. The pattern of similar genotypes in these Chinese families differs from that reported for western families.