Streptococcus mutans is a Gram-positive bacterium that lives in the mouth. The bacterium metabolizes different kinds of carbohydrates, creating an acidic environment in the mouth as a result of this process. This acidic environment in the mouth is what causes the tooth decay. S. mutans is considered to be the most cariogenic of all of the oral Streptococci . S. mutans is very important to study, not only because virtually everyone in the world carries it, but also because it has various symptoms that affect our daily lives. As the bacteria develop in the mouth, they cause tooth destruction, impaired speech, difficulty chewing, multiple infections, psychological problems such as low self-esteem, poor social interactions, concentration problems, etc. Though not fatal, tooth decay is one of the most common infectious diseases in humans. Also, cavities caused by the bacteria are the reason for half of all dental visits in the U.S. . The bacteria are most concentrated in the crevices, pits, and fissures that are a normal part of the teeth and surrounding structures. Adults may have a high concentration of S. mutans in their mouths. In contrast, infants and children have a smaller concentration, but they are more vulnerable to the bacteria . One of the important virulence properties of these organisms is their ability to form biofilms known as dental plaque on tooth surfaces. Biofilms are sessile bacterial communities adherent to a surface, and their formation occurs in response to a variety of environmental cues. S. mutans undergoes a developmental program in response to environmental signals that leads to the expression of new phenotypes that distinguish these sessile cells from planktonic cells (4). Microbiological studies have been conducted in particular in patients undergoing treatment for cancer. Radiotherapy-caused hyposalivation may affect the oral microbiota. Variations in quantity, complexity, and quality of the oral microbiota also occur during chemotherapy, leading to a major imbalance of the ecosystem (5).