T/F: Cariogenic species produce hydrogen peroxide.

• A. Depends on sugar availability
• B. False
• C. True
• D. Not sure

Answer: (B)

Hydrogen peroxide production in the dental plaque ecosystem is a trait seen in some aerobic or facultatively anaerobic commensal streptococci, such as Streptococcus sanguinis and Streptococcus gordonii. They generate H2O2 through enzymes like pyruvate oxidase when oxygen is present, and the resulting hydrogen peroxide helps suppress competing, often cariogenic, bacteria. Cariogenic species, notably Streptococcus mutans, are characterized by acid production and acid tolerance rather than hydrogen peroxide production; their metabolism does not rely on generating H2O2 as a key feature. Thus, saying cariogenic species produce hydrogen peroxide doesn’t fit the typical ecological roles of these bacteria, making the statement false.