Final answer:
The pH of plaque biofilm during the fermentation of fermentable carbohydrates by oral bacteria like Streptococcus mutans is acidic, usually around 4.0, which can contribute to tooth decay.
Step-by-step explanation:
The pH of plaque biofilm when fermentable carbohydrates are fermented is typically acidic, due to the production of organic acids such as lactic acid by bacteria like Streptococcus mutans. When these sugars, like sucrose from food, are broken down, glucose is used to form dextran for the biofilm structure, while fructose is fermented into lactic acid. This lactic acid production lowers the pH of plaque biofilm, which can lead to tooth enamel demineralization and tooth decay. The resulting pH of plaque biofilm can be close to 4.0, resembling the environment preferred by acidophilic bacteria.
In general, microorganism growth is highly dependent on environmental pH. Neutrophiles grow best near neutral pH but do not tolerate highly acidic conditions, while acidophiles thrive at a lower pH, often around 3.0. The acidic conditions within plaque biofilm created by fermentation favor the growth and survival of acidophilic bacteria.