MedMicroTest2streptococci

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victimsofadown
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MedMicroTest2streptococci
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2013-10-03 23:19:57
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MedMicroTest2streptococci
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  1. What are the general features of Streptococci? (gram reaction, motilitity, biochemical, shape, aeration, etc)
    • Gram+
    • Nonmotile
    • Catalase-negative
    • Ovoid to spherical in shape
    • Occur as pairs in hosts, chains when cultured
    • Ferment even when O2 is present
    • Complex nutrient requirements (blood agar to culture)
  2. What are the major diseases caused by streptococci? w/ causative agent(s)
    • 1. Acute infections of the throat and skin
    • Group A streptococci (eg S. pyogenes)
    • 2. Female genital tract colonization resulting in neonatal sepsis
    • Group B streptococci (eg S. agalactiae)
    • 3. Pneumonia, otitis media, and meningitis
    • S. pneumoniae
    • 4. Endocarditis
    • Viridans
  3. Describe the hemolytic classification of Streptococci
    • α hemolyitic: secrete H2O2 that change hemoglobin to to methemoglobin (ferrihemoglobin)
    • dark green pigment around colony
    • β hemolytic: streptolysin causes complete lysis of red blood cells
    • clear ring around colony
    • γ hemoltyic: cause no color change or lysis
  4. Describe (general) the Lancefield groupings
    • AKA Serologic groupings
    • Classifies Streptococci into groups A through U based on C-carbohydrate and capsular antigens
    • Includes all hemolysis types
    • Group specific antisera on latex beads are used for ID of β hemolytic streptococci
  5. General information about Streptococcus pyogenes
    • Group A
    • β hemolytic
    • One of the most frequently-encountered bacterial pathogens
    • Can invade intact skin and mucus membranes
    • Rapidly progressive infections ("skin eating")
    • Nasopharyngeal carriage is common
    • Habitat is ONLY humans - can be infection or normal flora on skin/mucus membrane
  6. What are the structural features involved in pathology or ID of Group A Streptococci
    • 1. Capsule: Hyaluronic acid forms the outermost layer
    • Capsule is non-immunogenic
    • 2a. Fimbriae: contain M protein (major virulence factor)
    • Destroys C3 convertase, preventing c3b opsonization
    • 2b. Group A-specific C-carboyhydrate: composed of rhamnose and N-acetylglucosamine
    • 2c. Protein F (Fibronectin-binding protein): mediates attachment to fibronectin in the pharyngeal epithelium
    • 3. Extracellular products: exotoxins (many can be produced)
  7. What are the exotoxins that can be secreted by Group A Streptococci?
    • pyrogenic exotoxins: superantigens, fever-inducing toxins
    • Streptolysin O and S: membrane-damaging toxin proteins that form pores in the bilayer
    • Streptokinase: lysis of fibrin clots
    • c5a peptidase: inactivates c5a (required for phagocytosis)
    • Streptodornase: hydrolysis of DNA outside or inside the infecting host cells
    • Hyaluronidase: unknown role
  8. Describe the steps of a S. pyogenes infection
    • Attachment to pharyngeal mucosa
    • May colonize without injury
    • May develop streptococcal pharyngitis (strep throat)
    • If sufficiently spread into bloodstream...
    • cellulitis: inflammation of subcutaneous tissue
    • fasciitis: inflammation of tissue under skin that covers underlying tissue
    • myonecrosis: death of muscle cells
  9. What are the potential infections/disease states that can occur from S. pyogenes (brief description )
    • 1. Acute pharyngitis or pharyngotonsilitis
    • Severe pus inflammation of the posterior oropharynx
    • 2. Impetigo
    • Severe superficial lesions on the face/limbs
    • 3. Erysipelas
    • Erythmia of face or lower limbs
    • 4. Invasive group A streptococcal (GAS) disease
    • Deep local invasion that can have necroizing fasciitis/myositis ("flesh-eating bacteria")
    • 5. Acute rheumatic fever
    • Autoimmune disease that occurs 2-3 weeks after pharyngitis initiation (after development of antibodies to M proteins react to heart and joint tissue)
    • 6. Streptococcal toxic shock syndrome
    • Streptococci in blood or normally sterile body site release pyrogenic exotoxins that act as superantigens, causing shock and multiorgan failure.
  10. What is scarlet fever?
    • A sunburn-like rash which develops as a result of S. pyogenes releasing pyrogenic exotoxin (integrated into genome by phage T12 via lysogenic conversion)
    • The patient does not have antibodies
  11. Describe the laboratory identification of Streptococcus pyogenes
    • Rapid latex antigen kits: group A streptococci will form a ppt to indicate presence
    • plating: small opalescent colonies surrounded by a large zone of β hemolysis on blood agar
  12. What are the treatments for S. pyogenes?
    • penicillin G is the antibiotic of choice for acute streptococcal disease (macrolides if patient has penicillin allergy)
    • Penicillin G + clindamycin are used for necrotizing fasciitis and streptococcal toxic shock syndrome
  13. General information about group B Streptococci? (Major species? hemolysis? location? Transmission?)
    • Streptococcus agalactiae
    • β hemolytic (less than group A)
    • GI tract normal flora, causes infection in vaginocervical tract and urethral mucous membranes
    • venereally (intercourse or giving birth)
  14. What does ELISA stand for?  What is it?  What is it used for?
    • Enzyme-Linked immunosorbent assay
    • Can demonstrate presence of bacterial antigen by using an anti-antibody which creates a color change when exposed to a specific substrate
    • Used to quickly determine if group B streptococci are present
  15. Why is S. pnuemoniae an important historical bacteria?
    It was involved in the transformation experiment by Griffith show that only encapsulated S. pneumoniae was pathogenic
  16. What are the basic properties of S. pneumoniae? (gram? motility? shape/structure? hemolysis? Other improtant features?)
    • Gram+
    • nonmotile
    • lancet-shaped cocci
    • tend to occur in pairs
    • α hemolysis (greenish zone) due to α hemolysin
    • Encapsulated (causes pathogenicity)
  17. Describe the epidemiology of Streptococcus pneumoniae
    • Obligate human parasite (extremely sensitive to environment) found in the nasopharynx as normal flora
    • Endogenous infection: carrier becomes susceptible after a general debilitation
    • Exogenous infection: by droplets from the nose of a carrier
  18. What are the S. pneumoniae features involved in pathology or ID of Group A Streptococci
    • Capsule: polysaccharide capsule that is antiphagocytic, but antigenic
    • Autolysin: peptidoglycan hydrolase in cell walls that lysis cell to release Pneumolysin
    • Pneumolysin: causes lysis of mammalian cell membranes
  19. What are the potential infections/disease states that can occur from S. pneumoniae (brief description)? Who does each most commonly affect?
    • 1. Acute bacterial pneumonia
    • An infection in the lungs causing the alveoli to fill with fluid or pus
    • Leading cause of death in the aged
    • 2. Otitis media
    • Characterized by earache
    • Most common bacteria infection of children
    • 3. Bactermia/sepsis
    • S. pneumoniae in the blood/sterile areas of the body
    • Most common in splenectomized individuals
    • 4. Meningitis
    • Inflammation of the meninges (high mortality rate even when treated)
  20. Describe the laboratory identification for Streptococcus pneumoniae
    • Culture: α hemolytic colonies appear (overnight, aerobic conditions, 37C)
    • Gram stain: lancet-shaped gram+ diplococci
    • optochin disc test: growth of colonies is inhibited by optochin, resulting in a ring of inhibition
    • Bile acids will causes cell lysis (turbidity indicates lysis)
  21. Describe the treatment of Streptococcus pneumoniae
    • Penicillin resistance has been increasing since 1980s
    • All are sensitive to vancomycin
    • Most remain sensitive to 3rd gen. cephalosporins
  22. Describe the prevention of Streptococcus pneumoniae infections
    • Pneumococcal polysaccharide vaccine (PPV): immunizes against 23 serotypes (causing 85% of infections) including penicillin-resistant strains
    • Pneumococcal conjugate vaccine (PCV7):
    • Made of 7 pneumococcal antigens conjugated to a nontoxic toxin
    • effective in infants/toddlers (6wk-5mo), causing dramatic decline in invasive pneumococcal disease
  23. Describe the viridans group
    • Streptococci
    • Includes many gram+, catalase neg, α or γ hemolytic species
    • Constitute main oral flora (typically avirulent) although S. mutans and others may cause dental caries

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