The Source of Infection in the Intrafamilial Transfer of Streptococcus mutans

Two approximal plaque samples were collected from each member of 32 families. Streptococcus mutans strains obtained from the samples were then characterized by bacteriocin typing. Only one S. mutans type was found in 15 (∼ 50%) of the families. In 10 of these, all members were infected with a single common type and in the remaining 5 families, all but 1 or 2 subjects harboured the organism. More than one S. mutans type was found in 12 (∼ 40%) of families; no individual harboured more than one type and usually no more than 1 member was S. mutans-free. In 4 of these families, maternal transfer was indicated, and in another 3, paternal transfer seemed likely; in 1, neither parent seemed to be the source of infection and in the remaining 4, the situation was not clear-cut. Overall, in 28 (88%) of the families, a common S. mutans type was shared by at least 2 members, 1 of them a parent. Thus, intrafamilial transmission of some strains of S. mutans can occur; the source of infection may vary from family to family and it was suggested that further investigation into the vehicle(s) responsible for indirect salivary transfer of the organism seems warranted.