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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)
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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
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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
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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
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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
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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)
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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
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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
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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 syndromeStreptococci in blood or normally sterile body site release pyrogenic exotoxins that act as superantigens, causing shock and multiorgan failure.
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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
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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
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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
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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)
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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
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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
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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)
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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
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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
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What are the potential infections/disease states that can occur from S. pneumoniae (brief description)? Who does each most commonly affect?
- 1. Acute bacterial pneumoniaAn 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)
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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)
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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
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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
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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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