Interaction between wild-type, mutant and revertant forms of the bacterium Streptococcus Sanguis and the Bacterium Actinobacillus Actinomycetemcomitans in vitro and in the gnotobiotic rat
Authors: J.D. Hillman, M. Shivers — Forsyth Dental Center, Boston, MA
Journal: Archives of Oral Biology | Published: 1988 | Vol. 33, No. 6: pp. 395–401
Abstract
In vitro, Streptococcus sanguis inhibits the growth of Actinobacillus actinomycetemcomitans, a presumed aetiological agent of localized juvenile periodontitis. When provided with glucose and good aeration, a growing culture of Strep. sanguis was found to produce hydrogen peroxide at concentrations exceeding the maximum LD₅₀ reported for strains of A. actinomycetemcomitans.
A mutant of Strep. sanguis was isolated that lacked the ability to produce α-haemolysis on blood agar. This mutant had less than 3% of its parent's level of pyruvate-oxidase activity and made no detectable hydrogen peroxide. In vitro, the mutant had also lost the ability to inhibit the growth of A. actinomycetemcomitans. A spontaneous revertant, isolated by its ability to produce α-haemolysis, was found to have regained parental levels of pyruvate-oxidase activity and hydrogen peroxide production, and could again inhibit A. actinomycetemcomitans in vitro.
Gnotobiotic Rat Model Results
A gnotobiotic rat model was used to demonstrate that Strep. sanguis and A. actinomycetemcomitans interact in vivo, and that this interaction depends on hydrogen peroxide production by Strep. sanguis.
| Challenge Organism | Mean A. actinomycetemcomitans (×10³ CFU/hemidentition) |
|---|---|
| Strep. sanguis wild-type (parent) | 14.0 ± 13.0 |
| Strep. sanguis H₂O₂-deficient mutant | 360.8 ± 164.4 |
| Strep. sanguis revertant | 9.2 ± 74.4 |
| Control (no Strep. sanguis) | 949.5 ± 1071.5 |
Conclusions
The level of A. actinomycetemcomitans colonization was approximately 70-fold lower in animals superinfected with wild-type Strep. sanguis than in control animals, and 25-fold lower than in animals infected with the hydrogen peroxide-deficient mutant. These results definitively demonstrate that hydrogen peroxide production by Strep. sanguis is the mechanism responsible for growth inhibition of A. actinomycetemcomitans both in vitro and in vivo — establishing the biological basis for the protective role of the ProBiora3® strains in periodontal health.
