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47 Cards in this Set
- Front
- Back
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Streptococci: cellular morphology
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Gram positive, form chains, have capsules. S. pneumoniae is diplococcal.
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Streptococci: biological properties
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colonies are smaller than staph
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Streptococci: culture needs
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require enriched media (blood agar)
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Name the most common clinical strains of Group A strep, and their most common carriers (4).
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S. pyogenes (children), S pneumoniae (children's nasopharynx, some adults), 3-4 S. agalactiae& enterococcus faecalis (colon).
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Streptococci: lab characteristics used to differentiate the groups of streptococci: Group A strep (4)
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Group A strep: 1 beta hemolysis (requires 1-2 days), 2 bacitracin susceptibility, 3 "rapid strep test" for antibodies against group A polysaccharide cell wall (high spec 95%, lower sens 80%), 4 antistreptolysin O (ASO) titer
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Streptococci: lab characteristics used to differentiate the groups of streptococci: S. pneumoniae. (4)
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1 alpha hemolytic, 2 zone of inhibition around optochin disc, 3 soluble in bile salts, 4 specific strain determined by Quellung reaction
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Streptococci: lab characteristics used to differentiate the groups of streptococci: Group A vs. Group B strep.
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Group B is not susceptible to bacitracin.
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Streptococci: lab characteristics used to differentiate the groups of streptococci: S. agalactiae (2)
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1 hydrolyze hippurate, 2 positive CAMP test, 3 narrower zone of beta hemolysis than GAS
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Describe the classification system of strep
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Classified by hemolysis pattern, then by clinical presentation, then subclassified by lettered groups A-O. (ie. Group A, B, C are all beta hemolytic). Group D is different because it's not even really strep.
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Streptococci: virulence factors: extracellular (5), cell surface (4)
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EXTRACELLULAR: 1 streptokinase, 2 streptodornase, 3 hyaluronidase, 4 pyrogenic exotoxins, 5 hemolysins. CELL SURFACE: 1 capsular polysaccharide, 2 M protein, 3 protein F, 4 lipoteichoic acid
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Which organism have we learned about that produces beta-lactamase?
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S. aureus
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What organism makes cheese?
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Strep
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Identify the hemolytic patterns of strep on sheep blood agar.
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BETA: complete hemolysis with a clear zone. ALPHA: incomplete hemolysis with a greenish zone. GAMMA: no hemolysis. ("beta is blasted, alpha is green like alphalpha, gamma is gone")
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Clinical presentations of strep? (3)
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1 pyogenic, 2 oral, 3 enteric
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Who made the lettered groups of strep, A-O? What characteristic is used to determine category?
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Lancefield. Based on C carbohydrate antigens.
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Name the group letter, Strep species, for beta-hemolyitic strep: primary human pathogen
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Group A strep. Strep. pyogenes.
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Name the group letter and Strep species for beta-hemolyitic strep: responsible for neonatal infections
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Group B strep. Strep. agalactiae. (the sad sick baby has no milk - agalactic.)
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Name the Strep group letter for beta-hemolyitic strep: infects animals
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Group C strep.
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Name the group letter and Strep speciesfor beta-hemolyitic strep: responsible for many infections, but especially UTI's.
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Group D strep. Enterococcus faecalis.
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Give the function of each of the extracellular virulence factors of Strep: 1 streptokinase, 2 streptodornase, 3 hyaluronidase, 4 pyrogenic exotoxins, 5 hemolysins
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1 streptokinase (digests fibrin), 2 streptodornase (digests DNA), 3 hyaluronidase, 4 pyrogenic exotoxins (superantigens that mediate circulatory shock), 5 hemolysins (destroys RBCs)
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Give the function of each of the cell surface virulence factors of Strep: 1 capsular polysaccharide, 2 M protein, 3 protein F, 4 lipoteichoic acid
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1 capsular polysaccharide (resists phagocytosis), 2 M protein (help colonization, resist phagocytosis by destroying C3 convertase), 3 protein F (binds fibronectin), 4 lipoteichoic acid (adheres to epithelial cells)
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Name the hemolysins of Strep and the systemic reactions that they produce. (2)
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1 Streptolysin O stimulates ASO antibodies, 2 Streptolysin S is cell-bound and non-antigenic
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CLINICAL APPLICATION: Scarlet Fever, pathophysiology: causing mechanism, symptoms (2), reinfection
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Strep pyogenes cause a throat infection, and then produce erythrogenic exotoxins. These act as superantigens and cause shock. Results in a red rash all over the body, strawberry tongue. Body produces antibodies that prevent reinfection.
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REVIEW: Describe the mechanism of superantigen presentation.
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results in non-specific activation of T-cells, result in huge amounts of interleukins (leads to 2-30% T-lymphocyte activation vs. <0.01%)
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Which is responsible for Toxic Shock Syndrome, Staph or Strep?
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Both. Strep TSS is usually associated with a bacteremia.
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Staph or Strep: TSS do you get from a tampon, TSS from minor trauma, TS-like syndrome, necrotizing fasciiitis
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Tampon TSS is from Staph aureus. Minor trauma TSS is due to streptococcal bacteremia. TSLS and necrotizing fasciitis are from Strep.
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REVIEW: CLINICAL APPLICATION: Why does toxic shock staphylococcus toxin (TSST) have such a strong effect?
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it is a superantigen
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Most common pathogen associated with UTI?
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E. faecalis
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How do strep disguise themselves?
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coat themselves in hyaluronidase capsules so they look like body cells
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CLINICAL APPLICATION: A child with a throat infection develops rheumatic fever. What pathogen is likely involved?
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Strep. Protein M, produced by strep, is structurally similar to heart muscle. molecular mimicricy.
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Strep: mode of transmission
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DIRECT CONTACT, droplets, fomites
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Name the diseases caused by Strep pyogenes.
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1 streptococcal pharyngitis, 2 impetigo, 3 scarlet fever, 4 erysipelas, 5 necrotizing fasciitis, 6 streptococcal TSS
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pyoderma: aka, def, mode of transmission, infected population
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aka impetigo. Purulent infection of the skin, vesicles > pustules. Spread by scratching. Young children with poor hygeine.
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erysipelas: def, group of strep involved
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group A strep, skin infection that breaks through to the dermis.
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necrotizing fasciitis: strep group, disease process
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group A strep. Cellulitis > bullae > gangrene > massive necrosis > multiorgan failure.
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S. pneumoniae: classification, morphology, major virulence factors (2)
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alpha hemolytic. Diplococcal. Major virulence factors are 1 capsule for avoiding phagocytosis, 2 cellular autolysin that is activated when it is dissolved by bile salts, 3 pneymolysin O
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pneumolysin O, fxn
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binds to cholesterol in membranes and creates pores
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S. pneumoniae: main carrier, means of transmission
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children > adults, usually in nasopharynx. Transmitted by human-human contact at daycares. Responsible for most community acquired pneumonia.
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S. pneumoniae: method of diagnosis
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CXR > culture for alpha hemolysis
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Normal streptococcus of the throat?
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Strep viridans.
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Quellung reaction, def
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When a specific strain of S. pneumoniae is placed on an antiserum, it swells. For distinguishing between the 90 serotypes of strep.
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Enterococcus faecalis: classification, distinctive characteristics, usual carrier, route of transmission
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Lancefield Group D although it is no longer classified as a Streptococcus. High resistance, tolerant to salt, heat, bile, and abx (including vancomycin). GI tract of humans and animals. Usual route is endogenous transmission.
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Enterococcus faecalis: at-risk populations
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At-risk pt's are those who 1 have been hospitalized for prolonged periods, 2 have been treated with broad spectrum abx (usually E. faecalis are resistant).
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VRE: acronym
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Vancomycin resistant enterococci. Have a plasmid that they can transfer to staphylococci.
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Strep. agalactiae: morphology, classification, most common disease, usual carriers
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S. agalactiae. Have capsules, form chains. Gram+ > catalase negative > beta hemolytic > group B > bacitracin resistant. Responsible for meningitis in newborn children. Carried in lower GI and GU tract.
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Describe the transmission of S. agalactiae to newborns.
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transient vaginal carriage in mother, colonizes newborn. Can develop disease 1 in utero, 2 at birth, 3 during first few months of life
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Name the viridans streptococci. (5) Classification?
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Alpha hemolytic. Strep. viridans, 2 mitis, 3 mutans, 4 sanguinis, 5 salivarium
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