Streptococcus mutans is a bacterium found in the human mouth. First identified in 1924 by J.K. Clarke, this microorganism is a gram-positive coccus, meaning it has a spherical shape and a specific cell wall structure. As a natural inhabitant of the oral cavity, it exists alongside at least 25 other species of oral streptococci and its presence alone is not an immediate cause for alarm.
This bacterium is a facultative anaerobe, which allows it to thrive in environments with or without oxygen. In the mouth, it shows a preference for colonizing the hard surfaces of teeth, particularly in the pits and fissures where it can be more sheltered.
The Role of S. mutans in Oral Health
Streptococcus mutans is a regular member of the oral microbiome, the complex community of bacteria, fungi, and other microbes that live in the mouth. The oral cavity’s microbial community is a delicate ecosystem where different species keep each other in check, maintaining a state of balance. This balance can be disrupted, leading to a condition known as oral dysbiosis.
A primary factor in this shift is diet, particularly the frequent consumption of fermentable carbohydrates. Such a diet creates an environment that favors the growth of acid-producing bacteria like S. mutans. This allows it to outcompete other, more benign bacteria and become a dominant species in the oral microbiome, which can lead to negative health consequences.
How S. mutans Causes Cavities
The process of cavity formation, or dental caries, is directly linked to the metabolic activity of Streptococcus mutans. This bacterium efficiently metabolizes sugars, particularly sucrose. When consumed, S. mutans ferments these sugars through a process called glycolysis, and a primary byproduct of this fermentation is lactic acid, which is secreted directly onto the tooth surface.
This acid production dramatically lowers the pH in the immediate vicinity of the bacteria. Tooth enamel, the hard outer layer of the teeth, is primarily composed of minerals like calcium and phosphate. When the pH on the tooth surface drops below a critical point (around 5.5), these minerals begin to dissolve out of the enamel in a process called demineralization.
S. mutans also produces sticky, long-chain sugar molecules called glucans from sucrose. These glucans act like a glue, allowing the bacteria to adhere firmly to the tooth surface and to clump together with other bacteria. This aggregation forms a resilient, structured community known as a biofilm, more commonly recognized as dental plaque.
The plaque biofilm creates a protective barrier for the bacteria, shielding them from the buffering effects of saliva and the physical force of brushing. Within this protected environment, the lactic acid produced by S. mutans becomes highly concentrated against the tooth enamel, accelerating the demineralization process and leading to the progressive breakdown of the tooth structure that defines a cavity.
Transmission and Colonization
The acquisition of Streptococcus mutans occurs early in life through social contact. The primary route is considered to be vertical transmission, which involves the transfer of the bacteria from a mother or primary caregiver to an infant. This often happens through saliva-sharing activities, such as sharing spoons, tasting food before feeding, or kissing.
Beyond the initial mother-to-infant transfer, horizontal transmission can also occur between other family members or close contacts. Colonization, where the bacteria establish a lasting presence, begins after the eruption of a baby’s first teeth. S. mutans requires a hard, non-shedding surface to effectively attach and form colonies, making newly emerged teeth an ideal habitat.
Managing S. mutans Levels
Controlling the population of S. mutans is centered on disrupting the conditions it needs to thrive. One method is dietary modification. Limiting the frequency and overall intake of sugars, especially sucrose, deprives the bacteria of their main fuel source. When S. mutans has less sugar to metabolize, it produces less acid, reducing the demineralization threat to tooth enamel.
Mechanical disruption is another strategy for managing this bacterium. The biofilm, or plaque, that S. mutans creates to protect itself is vulnerable to physical removal. Regular brushing and flossing are effective methods for physically breaking up and clearing away these bacterial colonies from tooth surfaces, which removes existing plaque and disrupts the formation of new biofilm.
The use of fluoride also helps manage the effects of S. mutans. Fluoride works in two distinct ways to protect teeth. It aids in the process of remineralization, helping to rebuild and strengthen tooth enamel that has been weakened by acid attacks, making the surface more resistant to future dissolution. Fluoride also has a direct inhibitory effect on the metabolic pathways of S. mutans, interfering with its ability to process sugar and produce acid, reducing its cavity-causing potential.