Chapter 4: Streptococcus

Group A Streptococcus represents a major human pathogen capable of causing acute suppurative infections including pharyngeal inflammation and localized tissue damage through the production of exotoxins, while also triggering delayed post-infectious sequelae such as rheumatic heart disease through immune-mediated mechanisms. Group B Streptococcus presents a particular concern in obstetric and neonatal medicine, as maternal colonization can result in serious infection in newborns during delivery. The Viridans group comprises alpha-hemolytic species that constitute normal oral microbiota but become clinically significant when bacteremia allows seeding of abnormal or damaged cardiac valves, leading to subacute endocarditis with characteristically slow progression compared to the aggressive destruction caused by aureus species. Group D organisms are subdivided into Enterococcus species, particularly faecalis and faecium, which have emerged as nosocomial pathogens with concerning resistance profiles including ampicillin and vancomycin resistance that complicate therapeutic options. Streptococcus pneumoniae receives comprehensive coverage regarding its pathogenic mechanisms, including the role of its polysaccharide capsule in evading phagocytosis, the epidemiology of penicillin-resistant strains, and strategies for preventing pneumococcal disease through immunization. The chapter integrates discussion of virulence factors, host immune responses, and antimicrobial resistance patterns across these clinically important organisms to provide students with a foundation for understanding streptococcal pathogenesis and clinical management.