wala strep.pptx
- 1. STREPTOCOCCUS WALA HASSAN MUSTAFA mS.C microbiology
- 2. CONTENT • General Characteristics • Classification of Streptococci • Morphology • Cultural characters • Pathogenesis & Virulence Factors • Group A Streptococcus (Streptococcus pyogenes) • Group B Streptococcus (Streptococcus agalactiae) • The Viridans Group (Alpha-Hemolytic Streptococci) • Streptococcus pneumonia (Alpha-Hemolytic Streptococci) • Enterococcus • Lab Diagnosis • CAMP TEST
- 3. General Characteristics of Streptococci • Gram-positive spherical/ovoid cocci arranged in long chains; commonly in pairs. • Non-spore-forming, nonmotile. • Can form capsules. • Facultative anaerobes • Most parasitic forms are fastidious and require enriched media. • Small, non pigmented colonies. • Sensitive to drying, heat, and disinfectants
- 4. • According to: • Hemolysis on Blood Agar- α, β, Ƴ • Lancefield classification- for β hemolytic streptococci, based on Carbohydrate antigen Classification of Streptococci
- 5. Classification • Classification system is based on hemolysis reactions. • β - hemolytic Complete hemolysis • Clear zone of hemolysis around colonie– A, B, C, D and G (S. pyogenes) • α – hemolytic, –Green discoloration around colonies S. pneumoniae and viridans • γ – hemolytic, No hemolysis– S.faecalis
- 7. • 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 Streptococci Group A S. pyogenes Group B S. agalactiae Group C S. equisimitis Group D Enterococcus Other groups (E-U) Lanciefield classification Lancefield Classification- β hemolytic
- 8. Morphology: The individual cocci are spherical or ovoid, 0.5-1 µm in diameter and are arranged in chains and pairs of up to 50 cells or more but stre.salivarius forms the longest chain. The length of chain vary widely with cultural conditions. Streptococci are gram positive Streptococci are non-motile and non-spore forming. Most species possess capsule.
- 10. Cultural characters : Aerobe & fac. anerobe-growing best at 37C—growth only in media with fermentable sugers, enriched blood /serum. Blood agar—incubet-24hrs—colonies are small-circular, semi transparent, low convex discs with an area of clear hemolysis around them. Colonies are glistening and look like dewdrops. Growth and hemolysis are promoted by10% Co2. Capsulated—mucoid colonies
- 11. • Structural components • M protein inhibits phagocytosis of bacteria • Lipo teichoic acid helps in adhesion of bactera • Capsule • Enzymes • Streptokinases- fibrinolysin • Deoxyribonucleases • Hyaluronidase • Pyrogenic / Erythrogenic exotoxin • Hemolysins • Streptolysin O- Oxygen labile, antigenic • Streptolysin S- serum soluble Facilitate spread of streptococci in tissues Pathogenesis & Virulence Factors
- 12. Group A Streptococcus = Streptococcus pyogenes • Beta-hemolytic • Infects the pharynx or skin • Often causes disease when normal microbiota are depleted • Spreads through respiratory droplets
- 13. Group A Strep- Virulence Factors 1. M protein of fimbriae • adheres to pharyngeal tissue • resists phagocytosis • 80 serotypes 2. Toxins • Streptolysin O and S - hemolysis • Erythrogenic toxin - rash • Pyrogenic toxin - fever 3. Enzymes • Deoxynuclease • Hyaluronidase • Streptokinase – lyse platelets, WBC • Help spread bacteria through tissue M protein
- 14. Group A Streptococcal Diseases 1. Pharyngitis (“strep throat”) • inflammation of the pharynx 2. Scarlet fever • rash that begins on the chest and spreads across the body 3. Pyoderma/Impetigo • confined, pus-producing lesion that usually occurs on the face, arms, or legs • Necrotizing fasciitis • toxin production destroys tissues and eventually muscle and fat tissue
- 15. Group B Streptococcus = Streptococcus agalactiae • Normally colonizes the lower gastrointestinal, genital, and urinary tracts Diseases Most often associated with neonatal bacteremia, meningitis, and pneumonia Immunocompromised older patients are at risk
- 16. Alpha-Hemolytic Streptococci: The Viridans Group • Alpha-hemolytic (“viridans = green”) • No Lancefield group • Lack group-specific carbohydrates • Normal microbiota • mouth, pharynx, GI tract, GU tract • Opportunistic Disease: • One of the causes of dental caries and dental plaques; produces dextran; leads to biofilm formation • Can cause meningitis and endocarditis
- 17. Alpha-Hemolytic Streptococci: Streptococcus pneumoniae • Gram-positive diplococcus • Alpha-hemolytic • Normally colonizes the mouths and pharynx • Can cause disease if travels to the lungs • Disease is highest in children and the elderly
- 18. Diseases caused by S. pneumoniae 1. Pneumococcal pneumonia – • bacteria multiply in the lower lung; cause damage to the alveolar lining; produce an inflammatory response • High fever; chest pain; SOB; sputum production • 85% occur after viral disease 2. Sinusitis and otitis media – • bacteria invade the sinuses or middle ear, often following a viral infection 3. Bacteremia and endocarditis – • bacteria in the bloodstream or in the lining of the heart 4. Pneumococcal meningitis – • bacteria that have spread to the meninges
- 19. Enterococcus • E. faecalis and E. faecium • Previously classified as group D streptococci but reclassified as a separate genus • Normal microbiota of the human colon • Opportunistic disease: • Urinary Tact Infection • Endocarditis • Common cause of nosocomial infections • Treatment: Difficult to treat due to resistance • Ampicillin and ceftriaxone • VRE - Vancomycin Resistant Enterococcus
- 21. Lab Diagnosis Sample:Throat swab, pus / swab, Joint fluid (arthritis), Blood (septicemia) etc, Gram Stain- Gram Positive in chains Culture on Blood agar- hemolytic colonies, catalase negative
- 22. 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
- 23. CAMP test • CAMP test- is a test to identify group B beta hemolytic Streptococci (str. aglactiae) based on their formation of a substance that enlarges the area of hemolysis formed by the beta hemolysin elaborated from staph. aureus. To detect the ability of an organism to produce the CAMP factor. (It is a biochemical test used to differentiate streptococcus from other beta- hemoltic streptococci).
- 24. • Principle: • Group B streptococci produce extracellular protein (CAMP factor) • CAMP act synergistically with staphylococcal -lysin to increase lysis of RBCs