T/F: Metabolism of ALL oral streptococci will result in lowering of environmental pH.

• A. False
• B. Unknown
• C. True
• D. Not sure

Answer: (C)

When oral streptococci metabolize sugars, they mainly run glycolysis to produce pyruvate, which is then reduced to lactic acid by lactate dehydrogenase. This reaction releases hydrogen ions into the surrounding environment, so plaque becomes acidic. In the mouth, repeated sugar exposure and the buffering limits of saliva mean this acidification lowers the pH of the environment, promoting enamel demineralization and selecting for acid-tolerant, cariogenic microbes. So, in the typical context of oral streptococci and caries biology, their carbohydrate metabolism tends to lower environmental pH, making the statement true. (Note that some bacteria can raise pH under specific conditions, but the common outcome relevant here is acid production.)