Microbiology Practice Exam

What bacterial species is primarily responsible for causing cavities in the human mouth?

1. Staphylococcus aureus

2. Escherichia coli

3. Streptococcus mutans

4. Lactobacillus casei

The correct answer is: Streptococcus mutans

Streptococcus mutans is primarily responsible for causing dental cavities, or caries, in the human mouth. This bacterium is a key player in the process of tooth decay due to its ability to ferment sugars, producing acid as a byproduct. The acid produced by S. mutans demineralizes the enamel, leading to cavity formation. It adheres well to tooth surfaces, particularly in the presence of dental plaque, where it can thrive in biofilms. While other bacterial species are present in the oral environment, they do not have the same level of association with cavity formation as S. mutans does. For example, Staphylococcus aureus is typically related to skin infections and other conditions, but not to dental caries. Escherichia coli is primarily found in the intestines and is associated with gastrointestinal infections. Lactobacillus casei, while it plays a role in various fermentative processes and can be involved in dental health, is not the primary agent in the initiation of cavities like S. mutans. Thus, the unique properties of Streptococcus mutans make it the leading cause of tooth decay in humans.