[Changes of bacterial flora on inbred mouse strains using experimental dental caries model].

Abstract

In the experimental dental caries model using inbred mouse strains, the bacterial flora of lower molars were investigated during the process of caries induction to examine the differences of bacterial flora between the caries susceptive mouse strains (BALB/cA, C57BL/6N) and the caries resistant mouse strain (C3H/HeN), as well as the relation between the bacterial flora and Streptococcus faecalis that seemed to be the pathogen of caries on this caries model. The total cultivable bacterial number immediately after weaning (3 weeks old) was larger in the caries susceptive strains than in the caries resistant strain. The composition of Gram(+) cocci, Gram(+)rods and Gram(-)rods varied in each strain and Gram(-)cocci were not isolated from any of the strains. The proportion of Gram(+)cocci to the total cultivable bacterial number was larger in the caries susceptive strains than in the caries resistant strain, while S. faecalis was the most predominant species in Gram(+)cocci in all strains. It suggests that S. faecalis existed indigenously on the lower molars of mice at the time of weaning (3 weeks old). The total cultivable bacterial number increased in all strains as feeding with Diet-2000 which contains 30% sucrose started. The number reached its peak on the fifth week, and it either remained the same or slightly declined after that. The number of S. faecalis also reached the peak between third and fifth week. The order of 10(5) - to 10(6) S. faecalis was isolated from the caries susceptive strains, and the order of 10(4) from the caries resistant strain throughout the experimental period. It suggests that C3H/HeN (the caries resistant strain) mice have certain caries resistant factors in the genetic background. Toward the end of the experimental period, S. acidominimus in the caries susceptive mice and Staphylococcus sciuri in the caries resistant mice increased and replaced S. faecalis. Gram(+)rods also increased in the caries susceptive strains. It seems that Gram(+)rods have some relation with the progress of advanced dental caries.