Streptococcus sanguinis-Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Streptococcus sanguinis-Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes


Streptococcus sanguinis is a Gram-positive, facultative anaerobic bacterium belonging to the genus Streptococcus. It is a commensal bacterium commonly found in the oral cavity, where it is part of the normal flora. S. sanguinis plays a crucial role in dental health, but under certain conditions, it can also contribute to opportunistic infections.


Morphology of Streptococcus sanguinis:
Cell Shape:It exhibits a cocci (round) morphology. The individual bacterial cells appear spherical.
Cell Arrangement:The cocci of S. sanguinis are typically arranged in chains. This chain formation is a characteristic feature of streptococci.
Gram Staining:S. sanguinis is Gram-positive. In the Gram stain, it retains the crystal violet stain, appearing purple under the microscope.
Size:The size of individual cells is relatively small, as is common for cocci bacteria. The size can vary, but they are generally in the range of 0.5 to 1.25 micrometers in diameter.
Capsule: Some strains of S. sanguinis may produce a polysaccharide capsule. The capsule can contribute to the bacterium’s virulence and ability to evade the host immune system.


Streptococcus sanguinis is primarily considered a commensal bacterium and an integral part of the normal oral flora. It typically contributes to oral health by competing with pathogenic bacteria for colonization sites and aiding in the prevention of dental diseases. However, under certain conditions and in specific host environments, S. sanguinis has the potential to exhibit pathogenic behavior. Here are key aspects of its pathogenicity:

Opportunistic Pathogen: S. sanguinis is generally opportunistic, meaning it can cause infection under particular circumstances, especially when there is a breach in host defenses or changes in the local environment.
Infective Endocarditis: While it is a rare occurrence, S. sanguinis has been associated with infective endocarditis. This is particularly relevant in individuals with pre-existing heart conditions, as the bacterium can enter the bloodstream during dental procedures and adhere to damaged heart valves.
Virulence Factors: S. sanguinis possesses virulence factors that contribute to its ability to adhere to surfaces and evade host immune responses. This includes surface adhesins that facilitate the attachment of the bacterium to host tissues.
Biofilm Formation: It is known for its capacity to form biofilms on tooth surfaces. While biofilm formation is generally associated with dental plaque and oral health, in certain situations, it can contribute to the development of infections, particularly on damaged heart valves.
Bloodstream Infections:In rare cases, S. sanguinis can cause bloodstream infections, especially in individuals with compromised immune systems or underlying health conditions.
Immune Evasion: The bacterium has mechanisms to evade the host immune system, allowing it to persist in the oral cavity and potentially cause infections in susceptible individuals.

Lab Diagnosis

The laboratory diagnosis of Streptococcus sanguinis involves a combination of microbiological techniques to identify and characterize the bacterium accurately. Here is a general overview of the steps involved in the lab diagnosis:

Sample Collection: Samples are collected from the suspected site of infection or colonization. In the case of S. sanguinis, this may include swabs from the oral cavity, dental plaque, or blood in instances of systemic infections.
Gram Staining: The initial step involves Gram staining of the collected sample. S. sanguinis is Gram-positive, appearing purple under the microscope. The Gram stain provides information about the cell morphology and arrangement.
Culture: The sample is cultured on appropriate agar media, such as blood agar. S. sanguinis is known for forming small, round colonies on blood agar. Culture allows for the isolation and growth of the bacterium.
Hemolysis Pattern: The hemolysis pattern on blood agar is observed. S. sanguinis typically exhibits alpha-hemolysis, where the colonies cause partial destruction of red blood cells, resulting in a greenish discoloration around the colonies.
Biochemical Tests: Various biochemical tests are conducted to confirm the identity of the isolated colonies as Streptococcus species. These may include catalase testing (negative for streptococci) and other species-specific tests.
Optochin Sensitivity Test: Streptococcus sanguinis is usually optochin-resistant.
Serological Tests: Serological tests may be employed for further characterization. This could include specific antisera to identify the Lancefield group (group A, B, C, etc.) to which the Streptococcus belongs.
Molecular Methods: Polymerase Chain Reaction (PCR) and other molecular techniques may be utilized for more precise identification and confirmation of Streptococcus sanguinis. Targeting specific genes can aid in species-level identification.
Antimicrobial Susceptibility Testing: Testing the susceptibility of the isolated strain to various antibiotics helps guide treatment decisions, especially in cases where the bacterium may be causing infections.


The treatment of Streptococcus sanguinis infections depends on the clinical context, the site of infection, and the severity of the condition. S. sanguinis is typically considered a commensal bacterium and contributes to oral health. However, in certain situations, it can cause opportunistic infections, particularly infective endocarditis. Here are general considerations for the treatment of S. sanguinis infections:

Infective Endocarditis: If S. sanguinis is causing infective endocarditis, antibiotic therapy is the primary approach. Antibiotics are administered to eliminate the bacterial infection. Commonly used antibiotics include:
Penicillin or ampicillin, often in combination with gentamicin.
Vancomycin may be used in cases of penicillin allergy.
Antimicrobial Susceptibility Testing: Before initiating antibiotic therapy, antimicrobial susceptibility testing should be performed to determine the susceptibility of the specific strain to antibiotics. This ensures the selection of an effective antibiotic.
Duration of Treatment: The duration of antibiotic treatment varies based on the severity of the infection and the response to therapy. Typically, a prolonged course of antibiotics, often several weeks, is required for the treatment of infective endocarditis.
Monitoring: Patients undergoing treatment for S. sanguinis infections, especially infective endocarditis, should be closely monitored for clinical improvement and potential complications. Blood cultures may be repeated to confirm bacterial clearance.
Preventive Measures: In cases where there is a risk of bacterial entry into the bloodstream (e.g., dental procedures in individuals with pre-existing heart conditions), prophylactic antibiotic treatment may be considered to prevent infective endocarditis. However, current guidelines have limited the use of prophylactic antibiotics, and decisions should be made based on individual risk factors.


Here are key preventive measures:

Oral Hygiene: Regular Brushing and Flossing: Brush teeth at least twice a day and floss daily to remove dental plaque, which is a biofilm that can harbor bacteria, including S. sanguinis.
Use of Antiseptic Mouthwash: Incorporate an antiseptic or antimicrobial mouthwash as part of oral hygiene routines to help reduce bacterial load.
Regular Dental Check-ups: Schedule regular dental check-ups and cleanings to detect and address any dental issues promptly. Professional cleanings help remove accumulated plaque and calculus.
Prompt Treatment of Dental Issues: Address dental problems promptly, such as cavities and gum disease, to prevent the progression of conditions that may contribute to bacterial overgrowth.
Prophylactic Antibiotics: In certain high-risk individuals with underlying heart conditions, prophylactic antibiotics may be considered before dental procedures that may cause bleeding. However, the use of prophylactic antibiotics is now more restricted, and decisions should be made based on individual risk factors and current guidelines.
Healthy Lifestyle: Maintain a healthy lifestyle, including a balanced diet, regular exercise, and adequate sleep. A strong immune system helps the body resist infections.
Avoiding Tobacco and Excessive Alcohol: Avoid smoking or using tobacco products, as these can contribute to oral health issues. Excessive alcohol consumption can also negatively impact oral health.
Limiting Sugary Foods and Beverages: Reduce the consumption of sugary foods and beverages, as these can contribute to the growth of bacteria in the oral cavity.
Education and Awareness: Educate individuals, especially those with heart conditions, about the importance of good oral hygiene and the potential risk of bacteremia during certain dental procedures.
Regular Blood Pressure Monitoring: For individuals with hypertension or other cardiovascular conditions, maintaining regular blood pressure monitoring and management is essential to prevent complications that may lead to infective endocarditis.
Proper Wound Care: For individuals at risk of infective endocarditis, proper wound care and infection prevention strategies are crucial. This includes attention to oral health and the prompt treatment of any oral injuries or infections.


Oral Commensal: Streptococcus sanguinis is a Gram-positive, facultative anaerobic bacterium that is primarily a commensal of the oral cavity, contributing to oral health by forming part of the normal oral flora.Chain-Forming Cocci: Microscopically, S. sanguinis appears as Gram-positive cocci arranged in chains, a characteristic feature of streptococci.Biofilm Formation: S. sanguinis is known for its ability to adhere to tooth surfaces and participate in the formation of dental biofilms. It plays a crucial role in the initial stages of dental plaque development.

Alpha-Hemolytic: On blood agar, S. sanguinis exhibits alpha-hemolysis, causing partial destruction of red blood cells and creating a greenish discoloration around the colonies.

Opportunistic Pathogen: While generally considered non-pathogenic, S. sanguinis can become opportunistic, causing infections, particularly infective endocarditis, in individuals with underlying heart conditions.

Virulence Factors: Possesses virulence factors that aid in adhesion to host tissues and evasion of the host immune system, contributing to its pathogenic potential in certain contexts.

Infective Endocarditis Association:It is commonly associated with infective endocarditis, a serious infection of the heart valves. It may enter the bloodstream during dental procedures and adhere to damaged heart valves.

Antimicrobial Susceptibility: Generally susceptible to antibiotics commonly used for streptococcal infections. Antimicrobial susceptibility testing is essential for guiding appropriate antibiotic therapy.

Preventive Measures: Prevention of S. sanguinis infections involves maintaining good oral hygiene practices, regular dental check-ups, and addressing dental issues promptly. Prophylactic antibiotics may be considered in certain high-risk situations.

Holistic Approach: The understanding of S. sanguinis encompasses its role in oral health, its potential opportunistic pathogenicity, and the importance of individualized preventive strategies tailored to specific risk factors and clinical contexts.

Further Readings

  • Title: “Streptococcus sanguinis: A Rare Cause of Infective Endocarditis.”Authors: Hussam Adi, Inas Kamal, and Mohammad El-Baba.
    Published in: Case Reports in Infectious Diseases (2018).
    DOI: 10.1155/2018/3960797
  • Title: “Streptococcus sanguinis induces neutrophil cell death by production of hydrogen peroxide.”Authors: Qian Li, Bingtao Su, et al.
    Published in: Cell Death & Disease (2018).
    DOI: 10.1038/s41419-018-0849-y
  • Title: “The Genomics and Proteomics of Biofilm Formation by Gram-Positive Bacteria.”Authors: Michael J. Walker, Paul S. P. Myint, et al.
    Published in: BioMed Research International (2015).
    DOI: 10.1155/2015/841605
  • Title: “Streptococcus sanguinis biofilm formation & interaction with oral pathogens.”Authors: Pushpa Pandiyan, Nirmala Rajendhran, and Rathinavelu Geetha.
    Published in: Future Microbiology (2018).
    DOI: 10.2217/fmb-2018-0155
  • Book: “Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases.”Authors: John E. Bennett, Raphael Dolin, and Martin J. Blaser.
    Publisher: Elsevier.
    ISBN-13: 978-0323482554
  • Book: “Bergey’s Manual of Systematics of Archaea and Bacteria.”Editors: William B. Whitman, Frederick Rainey, et al.
    Publisher: Wiley.
    ISBN-13: 978-1118960608
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