A spontaneous lactate dehydrogenase deficient mutant of Streptococcus rattus for use as a probiotic in the prevention of dental caries

Aims:  To study the ability of daily applications of Streptococcus rattus strain JH145 to affect the numbers of an implanted Streptococcus mutans strain in a rat model.
Methods and Results:  A spontaneous L(+)-lactate dehydrogenase (LDH)-deficient mutant of Streptococcus rattus , JH146, was isolated by screening on selective medium and compared with a previously isolated spontaneous LDH deficient strain, JH145. Both strains were shown to have single base pair deletion mutations in the structural gene ( ldh ) for LDH, and reversion frequencies were approximately the same. Animals treated once daily with ≥10⁶ CFU (colony forming units) of JH145 showed a statistically significant decrease in the proportion of implanted S. mutans to total cultivable bacteria in oral swab samples. The rate of decrease in S. mutans levels was dose-dependent. No adverse effects were observed by in-life observation of treated animals, and histopathological, haematological and blood chemistry analyses were unremarkable.
Conclusions:  The results presented indicate that daily application of JH145, a naturally occurring LDH-deficient variant of S. rattus , can compete with S. mutans for its habitat on the tooth surface.
Significance and Impact of the Study:  S. rattus JH145 has potential as a probiotic for use in the prevention of dental caries.