Streptococcus Prof Jyotsna Agarwal Dept Microbiology KGMU Streptococci

Streptococcus Prof. Jyotsna Agarwal Dept Microbiology KGMU

Streptococci Characters of Streptococci Gram positive cocci Size 1µm Chains or pairs Non motile Non spore forming Facultative anaerobes Fastidious Catalase negative

Classification of Streptococci According to: – Oxygen requirement Anaerobic (Peptostreptococcus) Aerobic or facultative anaerobic (Streptococcus) – Hemolysis on Blood Agar- α, β, Ƴ – Lancefield classification- for β hemolytic streptococci, based on C antigen

Hemolysis on Blood Agar Hemolysis on BA – -hemolysis Partial hemolysis Green discoloration around colonies e. g. S. pneumoniae & S. viridans – -hemolysis Complete hemolysis Clear zone of hemolysis around colonies e. g. Lancefield Group A & B (S. pyogenes & S. agalactiae) – -hemolysis No hemolysis e. g. Group D (Enterococcus sp. )

Hemolysis on Blood agar -hemolysis

Lancefield Classification- β hemolytic Streptococci Lanciefield classification Group A Group B Group C Group D S. pyogenes S. agalactiae S. equisimitis Enterococcus Other groups (E-U) Classification based on C- carbohydrate antigen of cell wall 20 Lancefield groups from A-H & K-V One or more species per group Group A- Further subdivided based on M, T, R protein (Griffith typing) in to 80 sertypes

Disease caused by S. pyogenes (Group A) Suppurative Non-Invasive Pharyngitis - inflammation of the pharynx, tonsillitis, otitis media, mastoiditis, rarely meningitis Pyoderma- Impetigo- localised pus-producing lesions usually occur on face, arms, or legs

Suppurative Invasive Erysipelas- diffuse infection of skin, involves superficial lymphatics. well demarcated borders Cellulitis- infection of skin & subcutaneous tissue, spreading

Toxin Mediated Diseases Scarlet fever- rash begins on chest & spreads across body Necrotizing fasciitis-Pyrogenic exotoxin produced by some trains of S. pyogenes- Can lead to DIC. Streptococcal Toxic Shock Syndrome

Non Suppurative complications or sequelae – Rheumatic fever: following pharyngitis carditis, poly arthritis, damage to heart valves potentially fatal – Acute Glomerulonephritits- following skin infection Immune complex mediated disease inflammation of glomeruli due to Ag-Ab complex deposit on basement membrane Clinically- Hematuria, Proteinuria, Hypertension Good prognosis

Pathogenesis & Virulence Factors Structural components – M protein inhibits phagocytosis of bacteria – Lipo teichoic acid helps in adhesion of bactera – Capsule- camouflages bacteria Enzymes – Streptokinases- fibrinolysin – Deoxyribonucleases – Hyaluronidase Facilitate spread of streptococci in tissues Pyrogenic / Erythrogenic exotoxin Hemolysins – Streptolysin O- Oxygen labile, antigenic – Streptolysin S- serum soluble

Lab Diagnosis Sample -Throat swab, pus / swab Gram Stain- GPC in chains Culture on Blood agar- beta hemolytic colonies, catalase negative

Bacitracin sensitivity Principle: – for presumptive identification of group A – distinguish between S. pyogenes from other beta hemolytic streptococci – Strep. Pyogenes sensitive to Bacitracin giving zone of inhibition around disk

Differentiation of -hemolytic streptococci – Lanciefield Classification – Bacitracin susceptibility Test Specific for S. pyogenes (Group A) – CAMP test Specific for S. agalactiae (Group B)- normal flora of genital tract in women, can cause neonatal meningitis

CAMP test Principle: – Group B streptococci produce extracellular protein (CAMP factor) – CAMP act synergistically with staphylococcal -lysin to increase lysis of RBCs

Summary Streptococcus general characters Lancefield Classification Toxins / Enzymes of S. pyogenes Infections / Sequelae caused Laboratory Diagnosis