Enhancing the Virulence of Streptococcus sobrinus in Rats

Abstract

The purpose of this study was to explore the virulence of strains of Streptococcus sobrinus that had been re-isolated from a desalivated rat. Furthermore, we wished to determine the influence of desalivation on the acidogenicity of fasting and sucrose-pulsed dental plaque in rats infected by strains of S. sobrinus. Experimental groups were formed and infected as follows: Group 1, desalivated animals, S. sobrinus ATCC 27352; Group 2, intact animals, infected as in Group 1; Group 3, desalivated animals, S. sobrinus re-isolated from a desalivated animal that had been infected with the ATCC 27352 strain for five weeks; Group 4, intact animals, infected as in Group 3; Group 5, desalivated animals, S. sobrinus re-isolated from a desalivated animal that had been infected with the ATCC 27352 strain for ten weeks; Group 6, intact animals, infected as in Group 5; Group 7, intact animals, no infection. All animals were fed cariogenic diet 2000 and sucrose-sweetened drinking water ad libitum. After five weeks, desalivated and intact animals that had been infected with isolates obtained from desalivated animals had significantly higher (p<0.05) smooth-surface-caries scores than did intact and desalivated animals infected with cultures of the original stock ATCC strain. Moreover, fasting plaque pH values were statistically lower in desalivated animals (Groups 1 and 3) than in intact animals (Groups 2, 6, and 7) (Tukey analysis, p<0.05). These data support the hypothesis that the pH values of plaque in desalivated animals are highly acidic and that lack of saliva may influence cariogenicity in at least two ways: the loss of inherent protective effects of saliva and the selection of cariogenic micro-organisms that exhibit enhanced virulence.