Streptococcus sanguinis is a species of Gram-positive, facultative anaerobic coccus bacteria. It belongs to the Viridans Streptococcus group, a collection of streptococci commonly found in the human body as part of its natural microflora.
Natural Habitat and Role in the Oral Cavity
Streptococcus sanguinis primarily resides within the human mouth, where it is a significant component of the oral microbiome. It acts as a pioneer colonizer, being among the first bacteria to adhere to tooth surfaces and initiate the formation of dental plaque. This initial attachment is facilitated by bacterial structures such as fimbriae and adhesins.
The relationship S. sanguinis has with its host is generally commensal, and at times, it offers beneficial effects. It plays a role in maintaining a balanced oral environment by competing with other bacteria that can cause cavities, such as Streptococcus mutans. This competition can involve the production of substances like hydrogen peroxide, or through metabolic processes like oxidizing thiocyanate to hypothiocyanite, which can inhibit the growth or activity of more cariogenic species. Studies have indicated that early colonization by S. sanguinis in infants can correlate with a delayed colonization by S. mutans, suggesting a protective influence against the development of dental caries.
Pathogenic Potential and Associated Conditions
While typically residing harmlessly in the mouth, S. sanguinis can become pathogenic if it enters the bloodstream (bacteremia). This can happen during routine activities like brushing teeth or during dental procedures that cause bleeding. Once in the bloodstream, this bacterium can travel to the heart, posing a serious threat.
The primary condition linked to bloodstream invasion by S. sanguinis is infective endocarditis, an infection of the heart valves or inner lining. S. sanguinis is recognized as one of the most frequent causes of infective endocarditis among oral streptococci, accounting for an estimated 18% to 30% of cases. The bacteria specifically colonize damaged heart valves, commonly the mitral and aortic valves.
Infective endocarditis develops when S. sanguinis adheres to pre-existing “vegetations” on the heart valves. These vegetations are composed of host components like fibrin and platelets, which form at sites of prior injury or abnormality on the valve surface. Once attached, the bacteria proliferate and become encased within these fibrin clots, forming a protective biofilm that can be difficult for the immune system and antibiotics to penetrate. This bacterial colonization and subsequent inflammatory response can lead to progressive damage and destruction of the heart valves, resulting in complications such as congestive heart failure, the formation of aneurysms, or even stroke if pieces of the vegetation break off and travel through the bloodstream.
Risk Factors and Prevention
Some individuals face a higher likelihood of developing infective endocarditis due to Streptococcus sanguinis and other oral bacteria. Risk factors include:
Pre-existing heart valve damage (e.g., from rheumatic heart disease or degenerative valve conditions)
Prosthetic heart valves
A history of previous infective endocarditis
Congenital heart defects
Implanted cardiac devices (e.g., pacemakers)
Intravenous drug use
Advanced age (over 60 years)
Compromised immune systems (e.g., due to chemotherapy or HIV/AIDS)
Prevention primarily centers on maintaining excellent oral hygiene to minimize the bacterial load in the mouth and reduce the chances of bacteria entering the bloodstream. This involves brushing teeth at least twice daily with fluoride toothpaste and cleaning between teeth daily using floss or other interdental devices. Regular dental examinations and professional cleanings are also recommended to ensure overall oral health and address any potential sources of infection. For patients at the highest risk of infective endocarditis, preventive antibiotics may be recommended before certain invasive dental procedures.
Diagnosis and Treatment
Diagnosing an infection caused by Streptococcus sanguinis, particularly infective endocarditis, involves identifying the bacterium in the bloodstream. The primary method for this is a blood culture, where multiple samples are collected over a period to confirm the presence of the specific bacteria. Imaging techniques like echocardiography are also used to visualize any vegetations or growths on the heart valves, which are characteristic signs of endocarditis.
Once S. sanguinis infection is confirmed, treatment usually involves antibiotics. For serious conditions like infective endocarditis, a prolonged course of intravenous antibiotics administered in a hospital setting is necessary. Penicillin G is a common choice, sometimes combined with an aminoglycoside like gentamicin, with treatment durations often lasting four to six weeks. Ceftriaxone may be used as an alternative antibiotic.
Throughout treatment, follow-up blood cultures are performed to ensure the infection has been cleared. In some complicated cases where antibiotic therapy alone is insufficient or if significant heart valve damage occurs, surgical intervention, such as valve replacement, may be required.