Bacteria of the species Streptococcus salivarius belong to the genus Streptococcus, to the division Firmicutes, to the class Bacilli and order of Lactic acid bacteria. They are physiologically present in the oral flora. However, especially for immunocompromised people, there is always a risk of infection due to colonization.
What is Streptococcus salivarius?
Streptococci are included in the bacterial domain under the division Firmicutes and assigned to the class Bacilli. They belong to the order Lactic Acid Bacteria or Lactobacillales and fall under it in the family Streptococcaceae. The genus Streptococcus includes several bacterial species. All species in the genus exhibit Gram-positive staining behavior. One species of Streptococcus is the short-chain species Streptococcus salivarius, which is actively non-motile. Previously, the bacterium Streptococcus thermophilus was cited as a subspecies of this species, which was then called Streptococcus salivarius subsp. thermophilus. The bacteria of the species Streptococcus salivarius colonize the human oral cavity in the form of saprophytes a few hours after birth, where they benefit humans more than they harm them. Like most other bacteria, however, they can cause neutropenia when carried into the blood, leading to sepsis (blood poisoning).
Occurrence, distribution, and characteristics
The genus Streptococcus includes several bacterial species that are approximately spherical in shape and usually arranged in chains. Members of the species Streptococcus salivarius are considered aerotolerant. This means that they can use oxygen for their metabolism, but are basically not dependent on it. Their metabolism is facultatively anaerobic and they can use alternative oxidants instead of oxygen in energy metabolism. The coccoid bacteria, like many other [[cocci],] grow in short chains. They are saprophytes that do not undergo chemo- or photosynthesis. They feed exclusively heterotrophically and consequently utilize organic, dead substances for energy and to build up endogenous substances. Energy-rich substances are broken down by them and converted into inorganic substances. In humans, saprophytes such as Streptococcus typically colonize internal and external body surfaces. Bacteria of the species Streptococcus salivarius colonize the human oral cavity immediately after birth.
Significance and function
Together with the related species Streptococcus sanguis, the bacteria of the species Streptococcus salivarius settle on the plaque of the teeth shortly after birth, where they produce an optimal environment for other cocci. These other cocci form the so-called oral flora or primary bacterial flora of the oral cavity. All cocci species maintain contact with each other and are capable of symbiotic relationships. For example, Streptococcus mutans extracts glycoproteins from food substances within saliva that can serve as food for other bacteria. Together with Streptococcus sobrinus, it forms a matrix with an anaerobic environment that prevents extraneous aerobic bacteria from colonizing the oral pharynx. Since bacteria of the species Streptococcus salivarius ultimately first prepare the living environment for the bacteria of the healthy oral flora and interact with these bacteria, they benefit humans. However, this is only true to a certain extent. Due to the fluid boundary between saprophytes and parasites, an organism of the species Streptococcus salivarius can, under certain circumstances, transform from a harmless co-inhabitant into a pathogenic parasite, especially for people with an immunological deficit. An infection that develops in this way is called an opportunistic infection. Moreover, since the infection in this case is due to bacteria from one’s own body flora, it is an endogenous infection. Accordingly, for healthy people with a strong constitution, the benefits of Streptococcus salivarius outweigh the risks, whereas older and otherwise weakened people are at risk of infection due to colonization.
Diseases and medical conditions
Bacteria such as Streptococcus mutans are best known as the bacteria that cause tooth decay. Colonization with Streptococcus salivarius also promotes colonization of teeth with the caries bacterium due to the symbiotic relationship of individual cocci species with each other.Together with Streptococcus sobrinus, these bacteria attach themselves to the primary flora on the teeth established by Streptococcus salivarius and find themselves in an ecological niche. The bacteria of the oral flora form lactate and other acids through the absorption of carbohydrates and sugars. The acidity of these acids lowers the pH environment in the oral cavity. The resulting acidic environment dissolves substances from the apatite lattice of the tooth enamel, especially carbonates, fluorine and phosphates. In this way, the enamel loses its hardness bit by bit, so that the teeth are more susceptible to initial caries. If the caries progresses further, we speak of enamel caries, pulp caries or dentine caries. The consequences of an actual infection with Streptococcus salivarius are far worse. This can occur, for example, if the bacteria are carried into the bloodstream. Such carryover is usually preceded by dental surgery, during which the bacteria can enter the bloodstream and cause bacteremia. For patients with strong immune systems, bacteremia is short-lived because their immune system fights and eliminates the microorganisms before they can spread throughout the body. In immunocompromised patients, bacteremia persists longer and, if left untreated, can progress to sepsis, which is often accompanied by a decrease in white blood cells. Sepsis is a life-threatening condition and corresponds to a systemic inflammatory response throughout the body. The bacteria also reach vital organs via the bloodstream. Thus, they can cause inflammation of the inner lining of the heart, for example.
