Oral streptococci are a diverse group of bacteria and a major component of the human oral microbiome. These microorganisms are among the first to colonize the mouth after birth, helping develop the microbial communities on the tongue, gums, and teeth. Their presence is a normal aspect of oral biology, found in virtually every person. As primary colonizers, they play a foundational role in shaping the oral cavity’s environment.
The Dual Role of Oral Streptococci
While “strep” is often associated with illness, most streptococci in the mouth are harmless or beneficial. They exist within a balanced oral ecosystem where many microbial species coexist. Some commensal species actively contribute to oral health. For instance, Streptococcus salivarius can produce compounds that inhibit the growth of more harmful bacteria, helping maintain a stable environment.
This contrasts with pathogenic species, such as Streptococcus mutans, which are known for their role in dental caries. It is also important to differentiate these resident oral bacteria from Streptococcus pyogenes, the bacterium responsible for strep throat, which is not a typical inhabitant of the oral microbiome. The balance between beneficial and potentially harmful streptococci is a significant factor in oral health.
Formation of Dental Plaque and Cavities
Tooth decay is a process heavily influenced by the oral bacterium Streptococcus mutans. This microorganism thrives on dietary sugars, particularly sucrose. When a person consumes sugary foods or drinks, S. mutans metabolizes these sugars and produces lactic acid as a byproduct, creating an acidic environment on the tooth surface.
In addition to producing acid, S. mutans uses sucrose to create a sticky polymer called glucan. This substance is a component of dental plaque, acting as a glue that allows the bacteria to adhere to the tooth enamel and form a biofilm. This plaque traps the acid produced by the bacteria against the tooth surface, preventing saliva from neutralizing it.
Prolonged exposure to this trapped acid damages the teeth. The acid leaches minerals like calcium and phosphate from the tooth enamel in a process called demineralization. Over time, this mineral loss weakens the enamel, leading to the formation of a cavity. The ability of S. mutans to create both acid and the protective plaque environment makes it efficient at causing tooth decay.
Connection to Systemic Health Conditions
The influence of oral streptococci is not always confined to the mouth. These bacteria can enter the bloodstream through activities like tooth brushing or flossing, especially if the gums are inflamed, or during dental procedures that cause bleeding. This entry of bacteria into the circulation is a temporary event known as transient bacteremia.
For most healthy individuals, the immune system clears these bacteria from the blood without issue. However, for people with pre-existing health issues, such as damaged heart valves or certain congenital heart conditions, this can pose a risk. Some species of oral streptococci, particularly Streptococcus sanguinis and Streptococcus gordonii, can attach to these damaged areas of the heart.
Once attached, the bacteria can multiply and form a protected cluster with platelets and fibrin, creating a vegetation. This can lead to a serious infection of the heart’s inner lining or valves, a condition called infective endocarditis. Bacterial adhesins, which are surface proteins, play a part in this attachment process, allowing the bacteria to colonize a site far from their original oral habitat.
Maintaining a Healthy Oral Microbiome
Promoting a healthy balance within the oral microbiome is more effective than trying to eliminate all bacteria. A primary factor in this balance is diet. Limiting sugary foods and processed carbohydrates reduces the fuel for acid-producing bacteria like S. mutans. A diet rich in fiber, fruits, and vegetables can help foster a more diverse and stable microbial community.
Effective oral hygiene is another practice for managing the oral microbiome. Brushing twice a day and flossing daily are mechanical actions that physically remove the plaque biofilm from tooth surfaces. This disrupts harmful bacteria before they can cause significant demineralization. Regular professional cleanings are also important to remove plaque and hardened tartar.
These practices work together to create an oral environment that favors beneficial bacteria. When harmful, acid-loving bacteria are kept in check through reduced sugar and consistent cleaning, commensal species have a better opportunity to thrive. This helps them outcompete pathogenic strains, contributing to a balanced oral ecosystem.