Lecture 3 Streptococcus pyogenes


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Lecture 3 Streptococcus pyogenes

  1. 1. ‫بسم ا الرحمن الرحيم‬ GENUS: STREPTOCOCCUS Prof. Khalifa Sifaw Ghenghesh
  2. 2. The Majority are Facultative Anaerobes. G +v Cocci Arranged in Chains, Some are Capsulated. Catalase: On Blood Agar: 1. β-Haemolytic Streptococci (Strep. pyogenes) 2. α-Haemolytic Streptococci (Strep. pneumoniae) 3. Non-Haemolytic Streptococci (Strep. Faecalis = Enterococcus faecalis).
  3. 3. A photomicrograph of Streptococcus spp.
  4. 4. Streptococcus pyogenes Lancefield Grouping > Haemolytic Streptococci by Serology > > Groups A-H & K-V. Group A = Strep. Pyogenes Griffith Types Lancefield Group A > by Specific Sera >> Types M, T, & R. Type M > 60 Serotypes > Type 1, Type 2, Etc..
  5. 5. VIRULENCE FACTORS A. Structural Components:> M-Protein > B. Extraceluular Products: Erythrogenic Toxins: > In Experimental Animals: Pyrogenicity, Cytotoxicity, Immunosuppresion, etc. Streptolysin O and Streptolysin S: Lysis RBCs. Streptokinase (Fibrinolysin): > Prevents the formation of an effective fibrin barrier Deoxyribonucleases (DNases): Hyalorunidase:
  6. 6. CLINICAL INFECTIONS Acute Sore Throat Impetigo Erysipelas Scarlet Fever Rheumatic Fever Acute Glomerulonephritis.
  7. 7. Inflammation of the oropharynx and petechiae, or small red spots on the soft palate caused by Streptococcus group A
  8. 8. LABORATORY DIAGNOSIS: A. By Direct Isolation & Identification: 1. Specimens: i. Throat Swabs > Patients with Sore Throat (Tonsillitis and /or Pharyngitis). ii. Throat and Nasal Swabs > Carriers (Outbreaks of Sore Throat or Scarlet Fever).
  9. 9. 2. Culture: > 2 Blood agar plates > If β - Haemolytic > Bacitracin sensitivity test > Sensitive >> Group A Streptococci. 3. Confirmation: > Lancefield's Serogrouping (Commercial Kits).
  10. 10. B. By Examination of Patient's Sera for Rising Titre of Antibodies to Streptococcal Antigens (e.g. RF or AGN): 1. Specimens: > Two Serum Samples are Collected in the Acute and Convalescent Stages. 2. Test: > The Antistreptolysin-O (ASO) Test. TREATMENT: S. Pyogenes > Penicillin G or Erythromycin
  11. 11. GROUP B STREPTOCOCCI Strep. agalactiae > A major Streptococcal Pathogen in Neonates and the Young Infants. 1. Early-Onset Infection:> Septicaemia 2. Late-Onset Infection: > Purulent Meningitis > Infection in Adults: GROUP D STREPTOCOCCI: Enterococcus faecalis