Epidemiology 

The epidemiology of Streptococcus oralis is the study of the distribution and determinants of the infection caused by this bacterium in human populations. Streptococcus oralis is a Gram-positive, rod-shaped, motile, and urease-positive bacterium that belongs to the Streptococcus mitis group, which is a heterogeneous group of oral streptococci that can cause various infections in humans, especially in the oral cavity and upper respiratory tract. 

Some of the epidemiological aspects of Streptococcus oralis infection are: 

• Prevalence: Streptococcus oralis is a commensal bacterium typically part of the human oral microbiota. It is found in high numbers in the oral cavity, especially on the tongue, teeth, and gingival crevices. It can also be detected in other sites, such as the nasopharynx, saliva, blood, and cerebrospinal fluid. The prevalence of Streptococcus oralis varies depending on the sampling method, site, and population. 
• Transmission: Streptococcus oralis, either direct or indirect contact, can result in the transmission of oral secretions or saliva. It can also be acquired from the environment or medical devices such as dental implants or catheters. The transmission of Streptococcus oralis may be influenced by factors such as oral hygiene, diet, smoking, alcohol consumption, and antibiotic use. 
• Risk factors: Streptococcus oralis is an opportunistic pathogen that can lead to infections in those with impaired immune systems and those who have blood tumours called haematological malignancies. The following are some risk factors for Streptococcus oralis infections: neutropenia (low white blood cell count), chemotherapy, radiation therapy, organ transplantation, HIV infection, diabetes mellitus, malnutrition, and old age. 
• Outcomes: Streptococcus oralis can cause serious complications such as bacterial endocarditis (infection of the heart valves), adult respiratory distress syndrome (a severe lung condition), streptococcal shock (a life-threatening drop in blood pressure), and urinary tract infections. The mortality rate of Streptococcus oralis infections can fluctuate between 10% and 50%, depending on the kind and degree of the infection, the patient’s underlying health, and the accessibility of the right therapy. 

Classification and Structure 

• Kingdom: Bacteria 
• Phylum: Firmicutes 
• Class: Bacilli   
• Order: Lactobacillales 
• Family: Streptococcaceae 
• Genu: Streptococcus  
• Species: Streptococcus oralis 

Streptococcus oralis is a Gram-positive, rod-shaped, motile, and urease-positive bacterium belonging to the Streptococcus mitis group. Its structure includes: 

• Cell wall: Peptidoglycan, teichoic acids, and lipoteichoic acids. It Contains proteins for adhesion, antigenicity, and enzyme activity. 
• Capsule: Some strains have a protective polysaccharide capsule aiding adhesion and biofilm formation. 
• Fimbriae: Hair-like appendages for attachment to host cells and biofilm formation. 
• Flagella: Whip-like appendages for movement. 
• Genome: 1,958,690 bp circular chromosome with 41.14% G+C content, closely related to S. mitis and S. pneumoniae. 

Antigenic Types 

The antigenic type of Streptococcus oralis needs to be better defined, as it does not belong to the Lancefield serological groups commonly used to classify streptococci based on their cell wall carbohydrates. The Lancefield groups include A to H, K to V, and others, but not all pathogenic streptococci can be identified by this method. Streptococcus oralis is usually considered a member of the Streptococcus mitis group, a heterogeneous group of oral streptococci with some phenotypic and genotypic characteristics. 

However, some studies have suggested that Streptococcus oralis may have some antigenic similarities with Streptococcus pneumoniae, a major cause of pneumonia and other invasive diseases. Streptococcus pneumoniae has more than 90 serotypes based on its capsular polysaccharide antigens; some are more virulent and antibiotic-resistant than others. Some strains of Streptococcus oralis have been found to express serotype three pneumococcal capsules, one of the most invasive and lethal pneumococcal serotypes. It may indicate that gene transfer can occur between oral streptococci and pneumococci, resulting in novel antigenic types and increased pathogenicity. 

Pathogenesis 

The pathogenesis of Streptococcus oralis is the process by which this bacterium causes disease in humans, a heterogeneous group of oral streptococci that can cause various infections in humans, especially in the oral cavity and upper respiratory tract. 

Some of the steps involved in the pathogenesis of Streptococcus oralis are: 

• Colonization: Streptococcus oralis is usually part of the human oral microbiota. However, it can also be an opportunistic pathogen that affects immunocompromised individuals and those with hematological malignancy (cancers that affect the blood). Streptococcus oralis must cling to the mucosal surfaces and create biofilms on the teeth, dental implants, or other medical devices to colonize the oral cavity. Streptococcus oralis can bind to oral mucins using multiple mechanisms, such as lectin-like interactions, sialic acid recognition, and fimbriae expression. Streptococcus oralis can also co-adhere with other oral bacteria, such as Streptococcus gordonii and Actinomyces naeslundii, to form complex biofilms. 
• Invasion: Streptococcus oralis can invade the host tissues and enter the bloodstream through various routes, such as dental procedures, trauma, surgery, or ulceration. Once in the blood, Streptococcus oralis can cause bacteremia (bacteria in the blood) and infective endocarditis (infection of the heart valves). Streptococcus oralis can also cross the blood-brain barrier and can bring about meningitis, infection of the spinal column, and the brain’s protective covering. Streptococcus oralis can create enzymes such as neuraminidase and IgA protease that can break down or alter parts of the host molecules involved in host defenses, allowing them to enter the host tissues and get past the host defenses. Neuraminidase can cleave sialic acid residues from glycoproteins and glycolipids, affecting host cell adhesion, signaling, and recognition. IgA protease can degrade IgA antibodies, which are essential for mucosal immunity. 
• Damage: Streptococcus oralis can cause serious complications such as bacterial endocarditis, adult respiratory distress syndrome (a severe lung condition), streptococcal shock (a life-threatening drop in blood pressure), and urinary tract infections. The damage caused by Streptococcus oralis may be due to direct effects of bacterial toxins or enzymes or indirect effects of host inflammatory response or immune-mediated damage. Some strains of Streptococcus oralis can express a capsule like the one produced by Streptococcus pneumoniae, which is a significant cause of pneumonia and other invasive diseases. The capsule comprises polysaccharides that can prevent the recognition and phagocytosis of Streptococcus oralis by immune cells. The capsule can also interfere with complement activation, a key component of innate immunity. 

Host Defenses 

Host defenses of Streptococcus oralis are the mechanisms the human body uses to protect itself from the infection caused by this bacterium. Streptococcus oralis is a Gram-positive, rod-shaped, motile, and urease-positive bacterium that can cause various human infections, especially in the oral cavity and upper respiratory tract. 

Some of the host defenses of Streptococcus oralis are: 

• Physical barriers: Mouth, nose, and throat mucous membranes, as well as their skin and lungs, act as barriers that prevent the entry of Streptococcus oralis and other pathogens. The saliva and mucus also contain enzymes and antibodies that can kill or inhibit the growth of bacteria. 
• Innate immunity: Innate immunity is the body’s initial defense in responding to foreign invaders. It consists of macrophages, neutrophils, natural killer cells, and dendritic cells that can recognize and destroy Streptococcus oralis and other bacteria. It also involves complement, cytokines, chemokines, and defensins that can activate or recruit other immune cells and enhance their functions. 
• Adaptive immunity: It is followed by the adaptive immune system that develops a specific and long-lasting response to Streptococcus oralis and other bacteria. B and T cells can produce antibodies and cytokines to neutralize or eliminate Streptococcus oralis and other bacteria. It also involves forming memory cells that can remember the previous exposure to Streptococcus oralis and other bacteria and mount a faster and more robust response upon re-infection. 

However, Streptococcus oralis can also evade or overcome some of these host defenses using various strategies. 

Clinical manifestations 

A Gram-positive bacteria known as Streptococcus oralis grows typically in chains. It has been identified as a member of the Streptococcus mitis group and is prevalent in the oral cavity. These pathogens are opportunistic and belong to this group. Signs and symptoms of Streptococcus oralis infection include a sudden, severe painful throat, swallowing discomfort, fever, red and swollen tonsils (often with white patches or streaks of pus), swollen lymph nodes, tiny crimson specks on the mouth’s roof, the front of the neck, and so on, difficulty feeding, sluggishness, limpness or weak muscle tone, difficulty breathing, irritability, jitteriness, seizures, rash, and jaundice. 

Diagnosis 

Diagnosing Streptococcus oralis infection can be challenging, as the conventional methods for other streptococci do not quickly identify this bacterium. Streptococcus oralis is a Gram-positive, rod-shaped, motile, and urease-positive bacterium belonging to the Streptococcus mitis group, a heterogeneous group of oral streptococci that share some phenotypic and genotypic characteristics. 

Some of the possible methods for diagnosing Streptococcus oralis infection are: 

• Rapid antigen test: Quick but not specific to distinguish between streptococci. 
• Molecular (PCR) test: Sensitive and accurate but requires specialized equipment. 
• Throat culture: Provides more information but takes up to two days for results. 
• Whole-genome sequencing: Most detailed, reliable, costly, and time-consuming. 

Control 

Strategies to control Streptococcus oralis infections: 

• Probiotics: Streptococcus salivarius 24SMB and Streptococcus oralis 89a can inhibit biofilm formation, modulate the immune response, and reduce inflammation. 
• Antibiotics: Use penicillin, amoxicillin, clindamycin, erythromycin, or vancomycin, depending on infection type and severity. 

• Prevention: Maintain good oral hygiene, avoid contact with infected individuals, wash hands frequently, clean wounds, and seek medical attention promptly if infection symptoms occur. 

References 

• Streptococcus oralis – an overview | ScienceDirect Topics