Many species of bacteria grow in the mouths of animals and can form biofilms on teeth (plaque). Within plaque, the outer layers contain high levels of oxygen and the layers closest to the tooth contain low levels of oxygen. The surface of the tooth is covered in a hard layer of enamel, which can be dissolved under acidic conditions. When the enamel breaks down, the bacteria in plaque can extract nutrients from the tooth and cause cavities. Certain types of bacteria (e.g., Streptococcus mutans) thrive in the innermost anaerobic layers of the plaque and are associated with cavities. Other types of bacteria (Streptococcus sanguinis) compete with S. mutans but are unable to thrive in acidic environments. Identify the biochemical pathway mutans uses for metabolizing sugar and describe how the pathway contributes to the low pH in the inner layers of plaque. Normal tooth brushing effectively removes much of the plaque from the flat surfaces of teeth but cannot reach the surfaces between teeth. Many commercial toothpastes contain alkaline components, which raise the pH of the mouth. Predict how the population sizes of mutans AND S. sanguinis in the bacterial community on the plaque between the teeth are likely to change when these toothpastes are used.

Biofilms are aggregated microorganism communities which are found attached to dental surfaces. Many species of bacteria such as the Streptococcus mutans and streptococcus sanguinis grow in the mouth of animals and form biofilms, also called dental plaque.

The S. mutans thrive in the Innermost anaerobic layer of the plaque due to their ability to metabolize sugar through the process of FERMENTATION. Because there is absence of oxygen in the Innermost layer of the plaque, glucose is transformed to lactic acid which lowers the pH of the inner layer of the plaque.

The use of commercial toothpaste can help remove or reduce plaques for the flat surfaces of the teeth. When alkaline toothpaste are used, the population of S. sanguinis will increase since they are able to survive in alkaline ( high pH) environment. The population of S. mutans will decrease since they can't survive in alkaline environment