Streptococcus mutans does not encode for the ________ gene and is unable to make hydrogen peroxide.

Streptococcus mutans does not encode for the ________ gene and is unable to make hydrogen peroxide.

• A. Lactate oxidase
• B. Catalase gene
• C. Peroxidase gene
• D. SpxB

Answer: (D)

Hydrogen peroxide production in oral streptococci relies on pyruvate oxidase, encoded by SpxB. This enzyme converts pyruvate to acetyl phosphate and, in the process, releases hydrogen peroxide. Streptococcus mutans lacks the SpxB gene, so it cannot carry out this reaction and therefore cannot synthesize hydrogen peroxide. The other options relate to enzymes that detoxify hydrogen peroxide (catalase and peroxidase) rather than produce it, so they don’t explain the lack of H2O2 production. While lactate oxidase could generate hydrogen peroxide in some systems, the well-established genetic basis for H2O2 production differences among oral streptococci centers on SpxB, making it the correct choice.

Hydrogen peroxide production in oral streptococci relies on pyruvate oxidase, encoded by SpxB. This enzyme converts pyruvate to acetyl phosphate and, in the process, releases hydrogen peroxide. Streptococcus mutans lacks the SpxB gene, so it cannot carry out this reaction and therefore cannot synthesize hydrogen peroxide. The other options relate to enzymes that detoxify hydrogen peroxide (catalase and peroxidase) rather than produce it, so they don’t explain the lack of H2O2 production. While lactate oxidase could generate hydrogen peroxide in some systems, the well-established genetic basis for H2O2 production differences among oral streptococci centers on SpxB, making it the correct choice.