Isolation and characterization of the substance isolated from Streptosporangium species which inhibits lactic acid production by oral bacteria.

1. The tentatively named MLI, which inhibits lactic acid production in mutants streptococci, was isolated from Streptosporangium species and purified by solvent extraction followed by chromatography, and then powdered. 2. MLI greatly inhibited pH-decline and lactic acid production in glucose-containing reaction mixture by mutans streptococci or Lactobacillus species. 3. These inhibitory mechanisms were not caused by an anti-bacterial effect, since the addition of a sufficient concentration of MLI to inhibit lactic acid production to the culture, recovery of cells in culture was not affected, excluding L. acidophilus. 4. MLI directly affected lactate dehydrogenase (LDH) activity. 5. These results indicate that MLI may represent a new anti-cariogenic substance.