Streptococcus dysgalactiae is a type of bacteria belonging to the Streptococcus genus. These bacteria are Gram-positive cocci, meaning they are spherical and retain a purple stain during a specific laboratory test, and they often grow in chains. While the genus Streptococcus includes many species, S. dysgalactiae is distinct from Streptococcus pyogenes, the bacterium widely recognized as the cause of strep throat. Despite their shared genus, each species presents unique characteristics and clinical relevance.
Where the Bacteria Is Found
Streptococcus dysgalactiae is a bacterium that commonly exists as a commensal organism, meaning it can live on humans without causing disease. It is frequently found in the upper respiratory tract, including the throat, and on the skin. This bacterium can also inhabit the alimentary and genital tracts in humans. Its presence on the skin is sometimes associated with existing skin conditions or breaks in the skin barrier.
This bacterium is classified within the beta-hemolytic streptococci, known for their ability to cause complete lysis of red blood cells. Human isolates often carry specific carbohydrate markers on their cell walls used for classification. The species is further divided into two subspecies: S. dysgalactiae subsp. equisimilis, predominantly associated with human infections, and S. dysgalactiae subsp. dysgalactiae, primarily found in animals.
Beyond humans, S. dysgalactiae is also found in various animal species. It is a known cause of bovine mastitis, an inflammation of the udder in cattle, and can lead to infectious arthritis in lambs, sometimes referred to as “joint ill.” While human-adapted strains are genetically distinct from those found in animals, its environmental presence highlights its broad ecological reach.
Associated Human Infections
Streptococcus dysgalactiae can cause a range of human infections, from localized skin issues to more serious conditions impacting internal body systems. The bacterium is increasingly recognized as a cause of disease. Superficial skin and soft tissue infections are among the more common presentations. These can include cellulitis, an infection causing redness, swelling, warmth, and pain in the skin, and erysipelas, a distinct form of cellulitis affecting the upper layers of the skin with well-defined raised borders.
Beyond non-invasive skin infections, S. dysgalactiae can also lead to more severe, invasive diseases. Bacteremia, an infection where the bacteria enters the bloodstream, can spread throughout the body. Individuals with bloodstream infections caused by this pathogen may experience fever, chills, and general malaise.
Invasive infections can also target specific sites, leading to conditions such as septic arthritis, an infection within a joint space causing intense pain, swelling, and reduced mobility. Osteomyelitis, an infection of the bone, can result from the spread of bacteria through the bloodstream or direct inoculation, leading to localized pain, swelling, and fever. Endocarditis, an infection of the heart’s inner lining, particularly the heart valves, can also occur, potentially causing fever, chills, and heart murmurs. The incidence of invasive S. dysgalactiae infections has been reported to be on the rise, sometimes approaching the rates seen with Streptococcus pyogenes.
Identifying At-Risk Individuals
Certain factors increase an individual’s susceptibility to Streptococcus dysgalactiae infections. Advanced age is a significant risk factor, with invasive cases clearly higher among the elderly population.
Underlying chronic medical conditions also predispose individuals to infection. People living with diabetes, cancer, or diseases affecting the heart or liver are more vulnerable. These conditions can weaken the body’s natural defenses, making it easier for bacteria to establish an infection.
Conditions that compromise the integrity of the skin barrier can also increase risk. Wounds, chronic ulcers, or skin conditions like eczema provide entry points for the bacteria to invade deeper tissues.
Individuals with weakened immune systems, often referred to as immunocompromised, represent another group at higher risk. This includes people undergoing immunosuppressive therapies or those with conditions that impair immune function, as their bodies are less able to fight off bacterial threats effectively.
Medical Diagnosis and Treatment
A definitive diagnosis of Streptococcus dysgalactiae infection requires laboratory analysis. When an infection is suspected, a healthcare provider will collect a sample from the affected site. This might include a blood sample for suspected bloodstream infections, tissue from a skin lesion, or fluid aspirated from an infected joint.
The collected sample is then sent to a laboratory where it is cultured on a special growth medium to allow the bacteria to multiply. Once sufficient growth occurs, laboratory technicians can identify the S. dysgalactiae bacterium through various laboratory tests.
Treatment for S. dysgalactiae infections primarily involves antibiotics. The bacterium is generally highly susceptible to penicillin, making it the preferred choice for therapy. Penicillin and related antibiotics work by interfering with the bacteria’s ability to build cell walls, leading to their destruction.
For patients who have a penicillin allergy, alternative antibiotics are available. Cephalosporins, a class of broad-spectrum antibiotics, are often effective. Clindamycin is another antibiotic that can be used in cases of penicillin allergy.