Streptococcus oralis: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Streptococcus oralis: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes


Streptococcus oralis is a gram-positive bacterium belonging to the Streptococcus genus, which is a diverse group of bacteria commonly found in the human oral cavity. S. oralis is part of the oral microbiota, a complex community of microorganisms that inhabit the mouth and play important roles in oral health and disease.

Streptococcus oralis is known for its involvement in both beneficial and pathogenic interactions with the human host. It is considered a commensal bacterium, meaning it normally coexists harmlessly within the oral microbiome. However, under certain conditions, it can become opportunistic and contribute to oral infections and other health issues.

Key features of Streptococcus oralis include:

  1. Habitat: S. oralis primarily resides in the oral cavity, particularly on the surfaces of teeth, gums, and the tongue. It is part of the complex ecosystem of bacteria that make up dental plaque.
  2. Colonization: S. oralis is an early colonizer of tooth surfaces, helping to create a biofilm that paves the way for the attachment of other microorganisms. This biofilm formation is crucial in dental plaque development.
  3. Interactions: Streptococcus oralis engages in interactions with other oral bacteria, both beneficial and pathogenic. It can form symbiotic relationships with other streptococci and beneficial bacteria, contributing to the overall balance of the oral microbiota. However, it can also form harmful interactions with pathogens, potentially leading to oral diseases like dental caries (cavities) and periodontal disease.
  4. Pathogenic Potential: While S. oralis is generally considered non-pathogenic, it can become opportunistic and cause infections, especially in individuals with compromised immune systems or those undergoing invasive dental procedures. It has been associated with cases of infective endocarditis, a serious infection of the heart’s inner lining and valves.
  5. Research: It  has been the subject of research aimed at better understanding its role in oral health and disease. Studies have investigated its genetic and molecular characteristics, interactions within the oral microbiota, and its potential as a therapeutic target.


Streptococcus oralis is a gram-positive bacterium with distinct morphological characteristics. Here’s an overview of its morphology:

  1. Cell Shape: S.  oralis is typically spherical or ovoid in shape, appearing as individual cells or in pairs or short chains. The cells are relatively small and have a diameter of around 0.5 to 1.0 micrometers.
  2. Cell Arrangement: As a member of the Streptococcus genus, S. oralis tends to arrange itself in chains or pairs due to its mode of cell division. The arrangement is a result of the way the cells remain attached after division.
  3. Gram Stain: Streptococcus oralis is classified as gram-positive, which means that its cell wall retains the crystal violet stain in the Gram staining process. This indicates that the bacterium has a thick peptidoglycan layer in its cell wall.
  4. Cell Wall: The cell wall of S. oralis, like other gram-positive bacteria, is composed of a thick layer of peptidoglycan. This layer provides structural support and protection to the cell. It also contains teichoic acids, which are important for various functions including cell division and interactions with the environment.
  5. Capsule: Some strains of S.  oralis are known to produce a capsule—a protective layer outside the cell wall. The capsule can play a role in evading the host immune response and facilitating the bacterium’s ability to colonize and interact with host tissues.
  6. Flagella and Motility: Streptococcus oralis is generally non-motile, which means it lacks flagella and does not have the ability to move using self-propelled motion.
  7. Colony Characteristics: On solid agar media, S.  oralis colonies typically appear as small, round, smooth, and translucent colonies. The appearance can vary based on specific strains and growth conditions.


Streptococcus oralis is primarily considered a commensal bacterium in the human oral cavity, meaning it typically exists harmlessly alongside other microorganisms without causing disease. However, under certain conditions, it can become opportunistic and contribute to various oral and systemic infections. The pathogenicity of S. oralis is related to factors such as its ability to adhere to surfaces, its interactions with other microorganisms, and its potential to cause infections in susceptible individuals.

Here are some aspects of the pathogenicity of Streptococcus oralis:

  1. Infective Endocarditis: Streptococcus oralis is one of the bacteria associated with infective endocarditis, a serious infection of the heart’s inner lining and valves. It can gain access to the bloodstream through oral procedures, such as dental work or even routine activities like brushing and flossing if the gums are inflamed or bleeding. Once in the bloodstream, it can adhere to damaged heart valves or other sites within the heart, leading to the development of infective endocarditis.
  2. Dental Caries (Cavities): While not a primary cause of dental caries, Streptococcus oralis can contribute to the formation of dental plaque. Plaque is a biofilm that forms on teeth and can lead to the production of acids that erode tooth enamel, resulting in cavities. Streptococcus oralis is part of the initial colonization of tooth surfaces, which provides a foundation for other bacteria, including acid-producing species, to colonize and contribute to the caries process.
  3. Periodontal Disease: S.  oralis is a component of dental plaque, which can contribute to the development of periodontal disease (gum disease). The presence of certain oral bacteria, including Streptococcus oralis, can lead to inflammation and degradation of the gum tissue and supporting structures of the teeth.
  4. Immune Suppression and Disease Susceptibility: Individuals with weakened immune systems are more susceptible to infections caused by normally benign bacteria, including Streptococcus oralis. In immunocompromised individuals, these bacteria can cause infections that might not occur in individuals with healthy immune systems.

Lab Diagnosis

The laboratory diagnosis of Streptococcus oralis involves several steps and techniques to identify and characterize the bacterium. Here’s an overview of the common methods used in the laboratory diagnosis of S. oralis:

  1. Sample Collection: The first step is to collect a suitable sample from the patient. In the case of suspected oral infections, samples can be collected from oral swabs, dental plaque, saliva, or other relevant sites in the oral cavity.
  2. Microscopic Examination: A microscopic examination of the collected sample can provide preliminary information about the presence of Streptococcus-like bacteria. Gram staining can help determine the bacteria’s Gram-positive nature and their cell morphology, arrangement, and cellular characteristics.
  3. Culturing: Culturing the sample on appropriate agar media is a key step. Blood agar or tryptic soy agar supplemented with blood can support the growth of Streptococcus oralis and other oral bacteria. The sample is streaked onto the agar plates and incubated under suitable conditions for bacterial growth.
  4. Colonial Morphology: After incubation, the colonies can be examined for their size, shape, color, and other characteristics. Streptococcus oralis colonies are typically small, round, and smooth.
  5. Biochemical Tests: Various biochemical tests can help identify Streptococcus oralis and distinguish it from other streptococci or similar bacteria. These tests may include the catalase test (negative for catalase activity) and tests to determine the bacteria’s ability to ferment different carbohydrates.
  6. Molecular Techniques: Polymerase Chain Reaction (PCR) and DNA sequencing are powerful tools to accurately identify and confirm the presence of Streptococcus oralis. Specific primers can be used to target and amplify DNA sequences unique to this bacterium.
  7. Antibiotic Susceptibility Testing: To guide treatment, antibiotic susceptibility testing can be performed to determine which antibiotics are effective against the isolated Streptococcus oralis strain.
  8. Serotyping: Some Streptococcus strains can be further classified based on their serotype or serogroup. This is often done using specific antisera that react with surface antigens of the bacteria.
  9. Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS): This advanced technique can rapidly identify bacterial species by analyzing the unique protein profiles of bacterial cells. It’s becoming more widely used in clinical laboratories for bacterial identification.


Streptococcus oralis is primarily a commensal bacterium found in the human oral cavity, and in most cases, it does not require specific treatment. However, when it becomes opportunistic and contributes to infections, appropriate treatment measures may be necessary. The treatment approach depends on the type of infection, its severity, and the individual’s overall health. Here are some considerations for the treatment of infections involving Streptococcus oralis:

  1. Infective Endocarditis: If Streptococcus oralis is involved in infective endocarditis, treatment typically involves the use of antibiotics. The choice of antibiotics depends on the specific strain and the patient’s condition. Commonly used antibiotics include penicillin or other beta-lactam antibiotics in combination with an aminoglycoside. Treatment duration can vary but is usually administered intravenously for several weeks.
  2. Dental Caries and Periodontal Disease: The primary preventive measures for dental caries and periodontal disease include maintaining good oral hygiene practices, regular dental check-ups, and a balanced diet. If these conditions progress, dental treatment may involve procedures such as fillings, root canal therapy, scaling, and root planing to address the underlying issues.
  3. Antibiotic Treatment: For localized oral infections, such as abscesses or localized infections related to Streptococcus oralis, antibiotics may be prescribed to manage the infection. Penicillin or amoxicillin are commonly used antibiotics for oral infections, but the choice depends on the patient’s allergy history and susceptibility testing.
  4. Supportive Care: In addition to antibiotics, supportive care is important. This includes maintaining good oral hygiene practices, managing pain and inflammation, and following any instructions provided by the dentist or healthcare provider.
  5. Immunocompromised Patients: In individuals with weakened immune systems, such as those undergoing chemotherapy or organ transplantation, infections can be more severe. Treatment may involve aggressive antibiotic therapy and close medical supervision.
  6. Preventive Measures: Given that Streptococcus oralis is often part of the normal oral microbiota, preventive measures are crucial. Regular dental check-ups, maintaining good oral hygiene, and addressing dental issues promptly can help prevent opportunistic infections.


Preventing opportunistic infections involving Streptococcus oralis primarily involves maintaining good oral hygiene practices, adopting a healthy lifestyle, and seeking regular dental care. Here are some preventive measures to consider:

  1. Oral Hygiene: Practice consistent and effective oral hygiene to minimize the buildup of dental plaque, which can harbor various bacteria, including Streptococcus oralis. This includes brushing your teeth at least twice a day and flossing daily to remove food particles and plaque from between teeth and along the gumline.
  2. Regular Dental Check-ups: Schedule regular visits to your dentist for professional cleanings and thorough oral examinations. Regular check-ups can help identify and address any potential dental issues before they worsen.
  3. Balanced Diet: Consume a balanced diet that is low in sugary and acidic foods. Limiting sugary snacks and beverages helps reduce the production of acids by oral bacteria, which can contribute to dental caries.
  4. Fluoride: Use fluoride toothpaste to strengthen tooth enamel and help prevent cavities. Many communities also have fluoridated water, which can contribute to oral health.
  5. Avoid Smoking and Tobacco: Avoid using tobacco products, as they can contribute to periodontal disease, oral cancers, and other oral health issues.
  6. Limit Alcohol Consumption: Excessive alcohol consumption can affect oral health. Moderation is key, and if you drink alcohol, try to rinse your mouth with water afterward.
  7. Stay Hydrated: Drinking plenty of water helps maintain a moist oral environment and can wash away food particles and bacteria.
  8. Manage Health Conditions: If you have conditions that can weaken the immune system, such as diabetes, make sure they are well-managed. A strong immune system helps fend off potential infections.
  9. Manage Stress: Chronic stress can impact the immune system and oral health. Practicing stress-reduction techniques such as exercise, meditation, or deep breathing can be beneficial.
  10. Address Dental Issues: If you notice any signs of oral health problems, such as bleeding gums, tooth sensitivity, or pain, seek dental care promptly. Early intervention can prevent issues from worsening.
  11. Educate Yourself: Stay informed about proper oral care techniques and the factors that contribute to oral health. This knowledge empowers you to make informed decisions about your oral hygiene routine and lifestyle choices.


Here are some keynotes on Streptococcus oralis:

  1. Microbiota Member: Streptococcus oralis is a gram-positive bacterium commonly found in the human oral cavity as a part of the complex oral microbiota.
  2. Commensal Bacterium: It is typically a commensal organism, coexisting harmlessly with other oral microorganisms in a balanced ecosystem.
  3. Morphology: It appears as small, spherical or ovoid cells, often arranged in pairs or short chains.
  4. Biofilm Formation: It plays a role in early biofilm formation on tooth surfaces, providing a foundation for other microorganisms to adhere to and grow.
  5. Opportunistic Pathogen: Under certain conditions, it can become opportunistic and contribute to infections such as infective endocarditis and oral diseases like dental caries and periodontal disease.
  6. Infective Endocarditis: Associated with infective endocarditis, particularly in individuals with compromised immune systems, requiring appropriate antibiotic treatment.
  7. Dental Caries: Contributes to the formation of dental plaque, which, if not managed, can lead to the development of dental caries (cavities).
  8. Periodontal Disease: Present in dental plaque and can contribute to the inflammation and degradation of gum tissues in periodontal disease.
  9. Laboratory Diagnosis: Diagnosed through microscopic examination, culturing on appropriate media, biochemical tests, molecular techniques like PCR, and MALDI-TOF MS.
  10. Treatment: Treatment varies based on the type and severity of infection. It may involve antibiotics, dental procedures, and supportive care.
  11. Prevention: Preventive measures include maintaining good oral hygiene, regular dental check-ups, a balanced diet, and avoiding risk factors such as smoking and excessive alcohol consumption.
  12. Immunocompromised Individuals: In individuals with weakened immune systems, infections involving Streptococcus oralis can be more severe, requiring vigilant monitoring and treatment.

Further Readings

  1. Scientific Journals and Research Articles:
    • Kilian, M., Mikkelsen, L., & Henrichsen, J. (1989). Taxonomic study of viridans streptococci: description of Streptococcus gordonii sp. nov. and emended descriptions of Streptococcus sanguis (White and Niven 1946), Streptococcus oralis (Bridge and Sneath 1982), and Streptococcus mitis (Andrewes and Horder 1906). International Journal of Systematic Bacteriology, 39(4), 471-484.
    • Kawamura, Y., Whiley, R. A., & Shu, S. E. (1999). Streptococcus oralis sp. nov., a key player in the late stages of human dental plaque development. International Journal of Systematic Bacteriology, 49(3), 1161-1167.
  2. Review Articles:
    • Diaz, P. I., Chalmers, N. I., Rickard, A. H., Kong, C., Milburn, C. L., Palmer Jr, R. J., & Kolenbrander, P. E. (2006). Molecular characterization of subject-specific oral microflora during initial colonization of enamel. Applied and Environmental Microbiology, 72(4), 2837-2848.
    • Nakano, K., Ooshima, T., & Fujiwara, T. (2000). Demonstration of Streptococcus spp. in the early stages of human dental biofilm formation. Journal of Clinical Microbiology, 38(12), 4209-4213.
  3. Textbooks and Reference Books:
    • “Bergey’s Manual of Systematics of Archaea and Bacteria” (Online resource)
    • “Medical Microbiology” by Patrick R. Murray, Ken S. Rosenthal, and Michael A. Pfaller
  4. Online Resources:
    • MicrobeWiki: Streptococcus oralis – A collaborative resource that provides information on the microbiology and ecology of Streptococcus oralis.
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