1. Chapter 23 – Streptococcus

2. Introduction Gram + cocci in chains Most are facultative anaerobes –Some only grow with high CO 2 Ferment carbs. to lactic acid Catalase (-) Complex nutritional requirements –Blood/Serum media

3. Classification schemes Serologic properties –Group specific Ag from cell wall –Important groups = A, B, C, F, G Hemolytic patterns –β-hemolytic –α-hemolytic Biochemical properties

4. Streptococcus pyogenes Group A strep β-hemolytic Virulence factors (Table 23-2)

5. Streptococcus pyogenes Epidemiology –Found in oropharynx & skin Mostly children and young adults Other Streptococcus species produce bacteriocins which suppress group A strep growth –Direct contact Infected mucus Body secretions of infected individual People without symptoms or on antibiotics are much less contagious

6. Suppurative diseases Pharyngitis (Strep throat) –2-4 day incubation –Impossible to visually disinguish strep throat and viral infection –Scarlet fever – complication of pharyngitis Diffuse, red rash Pyoderma (Impetigo) –S. aureus commonly present in infection –Fig. 22-7 Erysipelas – acute skin infection with systemic signs (fever, chills, etc.) –Fig. 23-3 Cellulitis

7. Suppurative diseases Bacteremia (~40% mortality) Necrotizing fasciitis (streptococcal gangrene) –Destruction of muscle, fat, and skin –Fig. 23-4 Streptococcus toxic shock syndrome (STSS) –Patients often have necrotizing fasciitis

8. Non-suppurative diseases Rheumatic fever –Results from pharyngitis (~10 days after) As many as 1/3 have mild or asymptomatic infections May be prevented with antibiotics –Inflammation in heart, joints, blood vessels, & skin –Affected individuals become more susceptible Acute glomerulonephritis

9. S. pyogenes ID Gram stain Blood agar plate –PYR enzyme = S. pyogenes or S. anginosus Antigen detection –Rapid Strep Test

10. Disease occurrence Noninvasive diseases are common – >10 million cases –Most common are pharyngitis & pyoderma Invasive diseases –4500 cases in 2004 – >500 STSS cases  45% mortality rate – >500 necrotizing fasciitis cases  25% mortality rate

11. Treatment & Control Penicillin Macrolides (erythromycin) Necrotizing fasciitis requires aggressive surgery People with history of Rheumatic fever may need preventative antibiotic therapy Wash hands & be considerate of others