Streptococcus sanguis are bacteria of the genus Streptococcus, which belong to the group of viridans streptococci and are a natural component of the human oral flora. The bacteria prevent the oral flora from being colonized by pathogenic bacteria and thus prevent caries, for example. If carried into the blood, however, the bacteria can cause inflammation of the inner lining of the heart (endocarditis).
What are Streptococcus sanguis?
Streptococci are a genus of different bacteria. They have gram-positive properties, a roughly spherical shape, and a mostly chain-like arrangement. Viridans streptococci are a subspecies of streptococci. They are not an actual species, but a group of different Streptococcus species with similar characteristics. Viridans streptococci are among the “greening streptococci” of the oral pharynx and for this reason are also called oral streptococci. For heart wall inflammation with slow progression, these bacteria are the number one bacterial pathogens, although most viridans streptococci are nonpathogenic. Veridans streptococci include the bacterial species Streptococcus sanguis. These streptococci are part of the natural flora of the oral mucosa and protect this area from pathogenic bacterial species. Nonetheless, the bacteria can cause serious illness with passage into the bloodstream.
Occurrence, distribution, and characteristics
The bacterial species Streptococcus sanguis is a natural inhabitant of the human oral cavity and, in this context, is found primarily in plaque. The bacterial species is facultatively anaerobic. Representatives of the species therefore grow optimally in the presence of oxygen, but can also survive in an oxygen-free environment by switching their metabolism. In an oxygen-free environment, they carry out fermentation and anaerobic respiration to obtain energy. That is, they oxidize organic substrates to CO2 and H2O. The energy gain of anaerobic cellular respiration is higher than the energy gain of pure fermentation metabolism. At 10 °C or less, growth no longer occurs. Even in nutrient media with 6.5% NaCl, the bacteria can no longer metabolize. The human body is the preferred habitat of the bacterial species, however, the bacteria also occur in animal plaque. All viridans bacteria have one thing in common: they are greening streptococci that exhibit α-hemolysis within the blood agar. So when the bacteria get into the blood, they attack the erythrocytes and break down the hemoglobin. This produces greenish products that have given the bacteria group its name. It is the streptococci of the species Streptococcus sanguis that, when they enter the blood, reach the heart via the bloodstream, where they can cause endocarditis. Viridans streptococci do not possess a polysaccharide capsule. Nor do they have Lancefield group C, A, or B antigens, which distinguishes them from other streptococci.
Significance and function
Basically, bacteria of the species Streptococcus sanguis are beneficial to humans. For example, colonization of the oral flora with streptococci prevents colonization of the same area with Streptococcus mutans. These bacteria are involved in the development of caries, as they form, on the one hand, adherent exopolysaccharides and, on the other hand, lactic acid, thus attacking the tooth substance. The presence of Streptococcus sanguis in dental plaque and oral flora makes the environment less favorable for the bacterial species Streptococcus mutans. Thus, in the broadest sense, Streptococcus sanguis prevent dental diseases such as caries. In other words, the bacteria do not live in the human oral flora at the expense of the host, but in a mutually beneficial relationship with the host. This distinguishes them from pathological parasites, which live at the expense of the host and harm the host organism in this way. However, the benefit of Streptococcus sanguis is exclusively within the oral flora. When carried into the blood, streptococci attack red blood cells and can reach other organs where they can cause disease.
Diseases and ailments
Various diseases can occur in connection with bacteria of the species Streptococcus sanguis. One of the most important diseases in this context is considered to be endocarditis, which corresponds to inflammation of the inner lining of the heart.The inner lining of the heart lines the heart cavities and portions of the veins and arteries near the heart and is structurally involved in the heart valve leaflets. Endocarditis is usually fatal if left untreated. In Western Europe, people rarely contract endocarditis since antibiotics were introduced. However, as nosocomially acquired infections caused by multidrug-resistant hospital germs have increased in recent years, cases of the disease have been on the rise again in the recent past, even in Western Europe. The spread of Streptococcus sanguis into the bloodstream can lead to endocarditis. In this context, operations of the oral cavity in particular should be mentioned as a risk factor. During such operations, bacteria from the natural oral flora can easily reach the bloodstream and eventually the heart. For this reason, preventive antibiotic therapy is now recommended to patients before and after oral surgery. In heart-healthy people, endocarditis is observed less frequently than in people with heart disease. In addition, the general and immunological constitution of patients plays an increased role in the development of lental endocarditis. Thus, in people with a good constitution, infection is prevented in time by the lymphoreticular system consisting of the liver, spleen, lymph nodes, and phagocytes in most cases. On the other hand, people weakened by immunology, disease or age are susceptible to infection. For this reason, lentic meningitis caused by bacteria of the species Streptococcus sanguis is particularly observed in AIDS patients, people with drug addiction, and people of older age.
