Streptococcus anginosus is a species of bacteria belonging to the Anginosus Group, which includes S. intermedius and S. constellatus. This bacterium is categorized as an opportunistic pathogen, meaning it typically lives harmlessly within the human body but has the capacity to cause severe disease. When the body’s natural defenses are compromised or breached, S. anginosus can transform into an aggressive invader.
Where Streptococcus anginosus Resides Naturally
Streptococcus anginosus is a common part of the human microbiome, existing as commensal flora across multiple body sites. Its primary residence includes the oral cavity, where it is often found in dental plaque and the upper respiratory tract. The bacterium also colonizes the entire length of the gastrointestinal tract and the urogenital tract. In these environments, its presence does not typically lead to illness in a healthy person.
This widespread colonization means the bacterium is constantly in contact with mucosal surfaces. Infection begins when the integrity of these protective barriers is broken, allowing the bacteria to move from their normal habitat into a sterile body site, such as the bloodstream or deep tissues. Dental procedures, gastrointestinal perforations, or underlying conditions like malignancy or diabetes can provide a route for invasion. This breach allows the bacterium to cause serious, deep-seated infections.
The Spectrum of Infections Caused
S. anginosus has a strong tendency to create pus-filled collections, known as abscesses, in various organs. This is due to the bacterium producing enzymes that liquefy tissue, helping it wall off the infection into localized pockets of pus. The formation of abscesses is a hallmark that sets the Anginosus Group apart from many other pathogenic streptococci.
These abscesses can develop in nearly any part of the body, often reflecting the bacterium’s original site of colonization. For instance, it is a significant cause of pyogenic liver abscesses, where it may be the most common bacterial culprit. Infections originating in the mouth or sinuses can spread to the central nervous system, leading to brain abscesses, a particularly dangerous manifestation.
The bacterium is also responsible for deep-seated soft tissue infections and intra-abdominal infections, often following bowel injury or surgery. Serious manifestations include infections of the chest cavity, such as empyema (pus collection in the chest wall space), and lung abscesses. When the bacterium enters the bloodstream (bacteremia), it can travel and initiate infections in distant organs, including the heart valves, causing a destructive form of endocarditis.
Identifying and Treating S. anginosus Infections
Identifying an infection caused by S. anginosus begins with a physician suspecting a deep-seated infection based on a patient’s symptoms and medical history. Diagnostic samples, such as blood cultures or aspirated fluid from a suspected abscess, are collected. These samples are then sent to the laboratory for culturing and identification.
Because these infections often involve deep organs, medical imaging is frequently required to precisely locate the site of the abscess. Computed tomography (CT) or magnetic resonance imaging (MRI) scans are used to visualize the collections of pus in areas like the liver, brain, or lung, guiding the subsequent treatment. Laboratory identification has become more precise with modern molecular techniques, which can accurately distinguish S. anginosus from other closely related species in the group.
Treatment relies on a dual approach: physical source control and systemic antibiotic therapy. Source control involves the surgical or radiological drainage of the abscess, which is necessary because antibiotics struggle to penetrate the thick, walled-off collection of pus. Following drainage, antibiotic treatment is initiated, often using high doses of penicillin, as most strains are highly susceptible. Laboratory testing confirms the bacteria’s sensitivity to ensure the correct medication is used, and treatment is typically prolonged, lasting several weeks, to ensure complete elimination.