Competitive properties of lactate dehydrogenase mutants of the oral bacterium Streptococcus mutans in the rat.

Prior establishment of a lactate dehydrogenase (LDH)-deficient mutant of Streptococcus mutans in the mouths of rats caused a 10-10,000-fold increase in the minimal infectious dose for persistent colonization by wild-type strains of this organism. The finding that LDH-deficient mutants can render their host relatively resistant to infection by decay-causing strains of Strep. mutans while being much less pathogenic themselves, lends support to their prospective usefulness as effector strains in the replacement therapy of dental caries.