The Effect of Oxygen on the Growth and Mannitol Fermentation of Streptococcus mutans

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Abstract
The effects of O2 on growth and mannitol fermentation of 8 strains of S. mutans were compared under aerobic and strictly anaerobic conditions. The growth of 3 strains was severely inhibited by O2; the others were O2-tolerant. The growth of 2 O2-tolerant strains was significantly enhanced by O2. The activities of superoxide dismutase and NADH oxidase in extracts from aerobically grown bacteria showed a positive correlation with the growth rate under aerobic conditions. The activities of these enzymes in O2-sensitive strains grown aerobically were as small as those in anaerobically grown cultures. Enzyme activities increased during aeration of anaerobically grown O2-tolerant strains, but not in O2-sensitive strains. In all strains, O2 changed mannitol catabolism from heterolactic to homolactic fermentation. Evidently, O2-tolerance of S. mutans depends on the ability of strains to induce NADH oxidase and superoxide dismutase.

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