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Doctor of Philosophy




In summary, the main points to support the view that dextran synthesis is unessential to the dental caries process are presented below:

1 . Dextran-fed, microbe-bearing rats do not experience dental caries.

2 . Lactobacillus casei 4646 has no extracellular dextransucrase enzyme or other extracellular enzymes which release glucose or fructose from sucrose .

3. L. casei 4646 does not synthesize extracellular polysaccharide of the dextran class when grown on sucrose-containing medium.

4. L. casei 4646 does not exhibit in vitro, adherent growth on stainless-steel wire when grown on sucrose-containing medium .

5. L. casei 4646 does not cause dental plaque formation on the molars of sucrose-fed gnotobiotic rats (Rosen, Lenney, and O'Malley, 1968).

6. L. casei 4646 induces dental caries of the pit and fissure class when introduced as a monoinfecting agent in sucrose-fed gnotobiotic rats (Rosen, Lenney, and O'Malley, 1968).

These observations advocated rejection of the hypothesis that extracellular dextran is an absolute requirement in the dental caries process. Therefore, dextranase will be an effective anticaries agent only against organisms such as Streptococcus E-49 (Fitzgerald, Keyes, Stoudt, and Spinell, 1968) which depend on the synthesis of dextran from sucrose for tooth colonization. This position predicts that dextranase treatment of sucrose-fed gnotobiotic rats infected with Lactobacillus casei 4646 would have no effect on the rats' caries experience.


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