Streptococcus species are Gram-positive cocci growing in pairs or chains, classified functionally into Group A (a wide range of clinical diseases) and Group B (leading causes of neonatal sepsis and meningitis). Group A streptococcal pathogenicity depends on a set of virulence mechanisms—exotoxins (proteases, hyaluronidase, DNase, streptokinase) that promote tissue invasion and spread, and anti-phagocytic surface structures (M protein, capsule) that evade immune clearance—while a distinct species, Streptococcus pneumoniae, is a major encapsulated cause of community-acquired pneumonia whose virulence and host defense (capsule versus C-reactive protein/complement activation) illustrate the general host-pathogen struggle between phagocytosis and immune evasion. This is a topic in medical microbiology concerned with bacterial classification, virulence mechanisms, and pathogen-host interaction.
Streptococcus species are Gram-positive cocci growing in pairs or chains, classified functionally into Group A (a wide range of clinical diseases) and Group B (leading causes of neonatal sepsis and m…