streptokokki

Streptococcus is a genus of Gram-positive cocci that typically occur in chains or pairs. They are facultative anaerobes and non–spore-forming, commonly colonizing the human throat, skin, and other mucosal surfaces. Classification relies on hemolysis patterns on blood agar and, for many species, the Lancefield serogroups (A, B, C, D, and others).

Among the best known groups are Streptococcus pyogenes (group A), Streptococcus agalactiae (group B), and Streptococcus pneumoniae (pneumococcus). S. pyogenes causes pharyngitis, impetigo, cellulitis, rheumatic fever, scarlet fever, and invasive diseases such as necrotizing fasciitis. S. agalactiae commonly colonizes the vagina and rectum and can cause neonatal sepsis, pneumonia, and meningitis. S. pneumoniae causes pneumonia, meningitis, and otitis media, and is notable for its polysaccharide capsule and vaccine-preventable disease.

Viridans streptococci are part of the normal oral flora but can contribute to dental caries and, in susceptible individuals, infective endocarditis. Other Lancefield groups (such as C and G) can also cause infections, particularly in patients with underlying conditions.

Diagnosis typically involves Gram staining and culture on blood agar to assess hemolysis, complemented by Lancefield grouping when indicated, rapid antigen tests, or PCR. Treatment generally uses penicillin or related beta-lactams; alternatives are available for those with allergies. Prevention focuses on vaccination against S. pneumoniae and maternal screening with intrapartum antibiotics to reduce group B streptococcal transmission. Carriage is common, and disease results from a combination of bacterial virulence factors and host susceptibility.