streptos

Streptos, short for Streptococcus, refers to a genus of Gram-positive, non-motile cocci that characteristically occur in chains or pairs. They are facultative anaerobes and are catalase-negative. Many species are part of the human microbiota, colonizing the oropharynx, skin, and gastrointestinal tract, while others are notable pathogens. They vary in virulence, disease spectrum, and habitat.

Classification and examples

Streptococcus species are commonly grouped by hemolysis on blood agar into alpha-hemolytic (partial hemolysis, greenish tint), beta-hemolytic (clear zones of complete hemolysis), and gamma-hemolytic (no hemolysis). Lancefield grouping uses cell wall carbohydrate antigens and classifies many pathogens into groups such as A, B, C, and others. Key pathogenic groups include group A Streptococcus (Streptococcus pyogenes) and group B Streptococcus (Streptococcus agalactiae). Streptococcus pneumoniae, the pneumococcus, is alpha-hemolytic and capsulated, and while not assigned to a Lancefield group, is a major cause of pneumonia, meningitis, and otitis media. Viridans streptococci are a heterogeneous, alpha-hemolytic group associated with dental caries and endocarditis.

Clinical relevance

Streptococci cause a wide range of diseases. Streptococcus pyogenes can cause pharyngitis, impetigo, cellulitis, necrotizing fasciitis, and streptococcal toxic shock syndrome, as well as non-suppurative sequelae such as rheumatic fever and post-streptococcal glomerulonephritis. Streptococcus agalactiae is a notable cause of neonatal sepsis and meningitis. Streptococcus pneumoniae causes community-acquired pneumonia, meningitis, and otitis media. Dental and systemic infections can involve viridans streptococci.

Diagnosis and treatment

Laboratory identification relies on Gram-stain morphology, hemolysis pattern, and species- or group-specific tests (bacitracin and optochin susceptibility, bile solubility, latex agglutination, PCR). Penicillin remains the cornerstone of therapy for many streptococcal infections; alternatives include cephalosporins and macrolides in penicillin-allergic individuals, with resistance patterns guiding choices. Vaccines exist for pneumococcus (PCV13, PPSV23), but no vaccine is currently available for most streptococcal species such as S. pyogenes. Prevention focuses on hygiene and, for certain species, pregnancy screening and neonatal care.