Streptococcus anginosus group

Streptococcus anginosus

Streptococcus anginosus group (SAG), also known as the Streptococcus milleri group, is a subgroup of the genus Streptococcus that consists of three distinct species: Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius. These bacteria are part of the normal flora of the human mouth, throat, digestive tract, and genitourinary tract, but they can become pathogenic under certain conditions, leading to a variety of infections.

Characteristics

The Streptococcus anginosus group is characterized by its ability to cause abscesses in various parts of the body, including the brain, liver, and lungs. These bacteria are facultatively anaerobic, gram-positive cocci that tend to form chains. They are different from other streptococci by their unique ability to ferment lactose and to produce a distinct type of hemolysis on blood agar plates, often described as "intermediate" between the clear beta-hemolysis and the green alpha-hemolysis.

Pathogenicity

While SAG species are commensal organisms in healthy individuals, they can become opportunistic pathogens, especially in people with compromised immune systems or underlying health conditions. The pathogenicity of these bacteria is attributed to their production of various enzymes and toxins that facilitate tissue invasion and immune system evasion. Infections caused by SAG can range from relatively minor, such as dental abscesses and tonsillitis, to severe, life-threatening conditions like bacteremia, meningitis, and deep-seated abscesses.

Diagnosis and Treatment

Diagnosis of SAG infections involves microbiological culture of specimens from the suspected infection site, followed by biochemical and molecular tests to identify the specific species involved. Treatment typically includes the administration of antibiotics, with the choice of antibiotic depending on the location and severity of the infection, as well as the susceptibility pattern of the isolate. Surgical intervention may be necessary to drain abscesses or manage complications.

Epidemiology

The epidemiology of SAG infections is not fully understood, as these bacteria are often overlooked or misidentified due to their close resemblance to other streptococci. However, they are increasingly recognized as important pathogens in both community and hospital settings, particularly in association with invasive infections.

Prevention

Prevention of SAG infections primarily involves maintaining good oral hygiene and promptly addressing any dental or periodontal issues. In hospital settings, strict adherence to infection control practices can help minimize the risk of nosocomial infections.