Lactate dehydrogenase mutants of Streptococcus mutans: isolation and preliminary characterization.

Mutants of Streptococcus mutans were isolated which lack the enzyme activity L (+)-lactate dehydrogenase. Reversion studies indicate that the genetic defects are in the structural gene for the enzyme. The mutants produce less titratable acid from glucose, adhere better to hydroxyapatite, and accumulate more plaque when grown in the presence of sucrose than does the parent strain. These findings suggest a possible use for the mutants as effector strains in the replacement therapy of dental caries.