A spontaneous lactate dehydrogenase deficient mutant ofStreptococcus rattusfor use as a probiotic in the prevention of dental caries

Abstract

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. 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 >or=10(6) 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. 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. S. rattus JH145 has potential as a probiotic for use in the prevention of dental caries.