Transmission and Establishment of Streptococcus mutans in an animal experimental system.

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S. mutans has been considered to be most significant pathogen in dental caries of humans and experimentalanimals. Several studies indicated that most people, with or without dental caries, harbor S. mutans. However, S. mutans was not detected in the oral cavity before the eruption of primary teeth. This infection with S. mutans seemed to be of intrafamilial transmission, especially from mother, based on serological and bacteriological similarity of S. mutans isolated from one mother and her children. The purpose of the present study was to investigate the influence of inoculum size in dam to litter transmission, incidence of dental caries and establishment of S. mutans in experimental animals.SPF female rats, which had harbored various number of S. mutans in their oral cavities, were made pregnant, and the transmission of S. mutans from dam to litter was examined. S. mutans MT8148R or 6715 was not recovered from the mandibles of 10 or 15-day old litter in any of the groups, however, both strains were recovered in 20-days old litter. There were positive correlations between the number of S. mutans recovered from the mandibles of litter and those of dam at weaning. Furthermore, positive correlations were shown between the occurrences and severity of caries of litter with S. mutans level of dam. The influence of inoculum size and infectious challenges on the establishment of S. mutans were examined in SD rats and ICR mice. The animals were infected with various inoculum sizes of S. mutans either once or 10 times. Infection of S. mutans with 10 challenges enhanced the establishment of S. mutans markedly in rats or mice, compared with that of one infection. The establishment of S. mutans was enhanced when the animals were fed with sucrose diet.