Multiple types of the bacterium Streptococcus mutans in the human mouth and their intra-family transmission.

To identify the source of infection with the potentially cariogenic Streptococcus mutans, unstimulated saliva and two approximal plaque samples were examined from each member of 10 families, five of which were re-sampled 6 months later. Each morphological type of Strep. mutans appearing on SB-20 medium was identified by a biochemical micromethod and by bacteriocin typing. Ninety-three per cent of the 46 subjects harboured Strep. mutans and multiple types were detected in 78 per cent of adults and 46 per cent of infected children. Each mouth yielded c/e/f biotypes and 46 per cent also carried d/g types. Generally, saliva types were the same as those in plaque and the second sampling confirmed the first. Most fathers did not share strains with others in the family but all the infected children shared at least one common strain with the mother. The mother as the major source of Strep. mutans infection in young children was confirmed.