The bacterium Streptococcus mitis belongs to the viridans streptococci. Viridans streptococci are found predominantly in the mouth and throat.
What is streptococcus mitis?
Mitis bacteria are gram-positive and belong to the streptococcus bacterial genus. Streptococci are spherical bacteria that prefer to be arranged in chains. Gram-positive bacteria can be stained blue in the Gram stain. They have a cell wall to which a thick, multilayered murein envelope is attached. On blood agar, viridans streptococci form a green halo. This is a typical sign of α-hemolysis and has given the cocci their name. Viridans comes from Latin and means “producing a green color.” Streptococcus mitis stops showing growth at temperatures below 10° Celsius. At 45° Celsius, on the other hand, the pathogen can still multiply well. The mitis group as a subgroup of the viridans streptococci is also called the sanguis group in the medical literature. The pathogenicity of the α-hemolytic group streptococci has long been underestimated. The ß-hemolytic groups were feared because of the severe diseases they could cause. However, pathogens from the α-hemolytic group can also cause severe disease. Therefore, they are called opportunistic or facultative pathogens. Opportunistic bacteria are harmless in a healthy person. However, they take advantage of a weakness in the immune system to cause infection. Such an infection is also called an opportunistic infection.
Occurrence, distribution, and characteristics
Streptococci of the Mitis group live in the oral cavity of humans. They are also found in the ear, nose, and throat. In rare cases, the bacteria are also found in other areas of the body, such as the skin. Streptococcus mitis has also been detected in the dental plaque of various animal species. The bacteria are transmitted by direct contact. Almost every person in adulthood has streptococci of the mitis group in his or her mouth. Streptococci can therefore also play a role in bite injuries. In this context, the risk of infection is highest in human bites. Around 50 percent of all bite wounds caused by humans lead to infection. Bite wounds that are particularly close to the joints and deep bite wounds often become infected. Therefore, when antibiotics were not yet available, the consequences of a human bite were drastic. If medical care was provided within the first hour after the bite, amputation had to be performed in ten percent of all cases. If medical care was not available until later, the amputation rate increased to over 30 percent. Animal bites lead to infection in only about 20 percent of cases.
Diseases and complaints
Streptococcus mitis is also only facultatively pathogenic in the oral cavity. In healthy people, the bacteria are part of the physiological oral flora. Under certain conditions, however, Streptococcus mitis can increase caries formation. High sugar consumption has a favorable effect. Caries is also known colloquially as tooth decay. It is a multifactorial disease of the tooth. Bacteria metabolize carbohydrates from food into acids. The acids dissolve calcium phosphates from the tooth enamel, resulting in demineralization in the long run. Initially, white spots form on the enamel. When color pigments from food are deposited in these spots, they turn dark. If remineralization does not occur at this stage, the disease progresses to the dentin. Dental caries can cause toothache because the dentin is much softer than the enamel, so the caries can spread widely at this level. In so-called caries profunda, deep dental caries, the lesion has progressed into the tooth pulp. This stage is associated with severe tooth pain. The tooth often cannot be saved at this stage and must be removed. Mitis streptococci can enter the blood through injuries in the oral cavity, for example after dental surgery. Hematogenous spread can cause bacterial vegetations with Streptococcus mitis to form on the heart valves. These lead to permanent inflammation of the inner lining of the heart. The inner lining of the heart, the endocardium, lines the entire interior of the heart and also forms the valves.Endocarditis lenta develops during infection with Streptococcus mitis. Endocarditis lenta is a subacute variant of bacterial endocarditis. The disease usually begins insidiously. Symptoms are rather nonspecific. Affected individuals develop fever of unclear cause and generally feel rather weak. They have no appetite and are pale. Anemia is often present. This results from the adhesions of the heart valves, where many red blood cells are destroyed during the passage of the heart valves. In later stages, drumbeat fingers and clock glass nails may develop due to the lack of oxygen caused by anemia. Drumbeat fingers are conspicuous by rounded distensions of the finger end links. Clock glass nails are caused by connective tissue hypertrophy in the nail bed. The nails are strongly curved in the transverse direction and in the longitudinal direction. Minute cardiac-related emboli cause lentil-sized, bluish painful nodules on the fingers and toes. These are also known as Osler nodules. They are a typical symptom of bacterial endocarditis. When individual bacteria or groups of bacteria become detached from the heart valves, they can travel through the bloodstream to other organs and cause secondary diseases. Because of the risk of developing bacterial endocarditis, pre- and post-operative care is provided during scheduled dental procedures, for patients at increased risk of endocarditis. Thus, patients receive antibiotics approximately one hour before and a few hours after treatment. High-risk patients include those with heart valve replacements, patients with a congenital heart defect, and patients with heart transplants.
