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40 Cards in this Set
- Front
- Back
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What are the significant diseases caused by streptococcus?
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Scarlet fever, rheumatic heart disease, necrotizing fasciitis, and pneumonia
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What is beta hemolysis?
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complete lysis of RBCs on blood agar plates with a zone of clearing seen in several strep species but other bacteria as well (e coli, staph aureus)
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What is alpha hemolysis?
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Incomplete lysis of RBCs with a zone of greening; only seen in streptococci
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What is the Lancefield classification system?
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System which classifies beta hemolytic bacteria into different groups
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What is the 1 species in Group A?
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streptococcus pyogenes
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What is the 1 species found in group B?
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Known mostly as "Group B strep"; s. agalactiae
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What species are found in group D?
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Enterococcus species
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Describe the gram stain, oxygen requirements, and catalase status of streptococcus
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Gram + that grow in chains (or pairs for s. pneumonia), strictly fermentative, and catalase negative
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Where is group B strep normally found and what disease is it known to cause?
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It is normal flora of the intestine but can spread to the vagina and cause neonatal meningitis in babies born to a mother with a group B positive vagina
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In what population is found infective group D strep?
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Hospitalized patients
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Describe problems with group D strep
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They are resistant to penicillin with increasing resistance to VRE
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Group C/G strep are generally normal flora in what location?
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Upper respiratory tract, intestines, vagina, and skin
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What are two examples of alpha hemolytic strep?
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Strep pnemoniae and strep viridans group
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Where is strep viridans normal flora and how can it be transmitted?
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It is normal in the oral cavity and can enter the blood after dental procedures
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Describe the cell wall of Strep pyogenes
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It is gram + with teichoic/lipoteichoic acid, peptidoglycan, M protein, and G protein
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What is the M protein?
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The major protein antigen and virulence factor of Strep pyogenes; inhibits complement activation
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If antibodies are developed against the M protein of Strep pyogenes, how is it that one could become reinfected?
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There are a large number of serotypes of the M protein and antibodies are only protective against the one
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What is significant about the G protein of Strep pyogenes?
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It binds the Fc portion of Ig backwards and thus inhibits opsonization
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How are Strep pyogenes resistant to phaocytosis?
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They have a polysaccharide capsule and the M protein inhibits complement fixation, rendering it resistant to opsonization and phagocytosis
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What are the two types of exotoxins secreted by strep pyogenes?
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cytolytic toxins (streptolysin O and S) and pyrogenic toxins (superantigens Spe A and C)
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What is the function of streptolysin A and in what environment does it function?
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It is able to kill phagocytic cells, it only functions in an anaerobic environment (oxygen labile)
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What are differences between Streptolysin O and S?
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S can function in aerobic environments, whereas O cannot
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What is the main symptom of pyrogenic toxins?
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They produce fever
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Which toxins cause toxic shock syndrome?
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pyrogenic exotoxins (superantigens)
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What type of toxins cause the rash of scarlet fever?
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Erythrogenic toxins, which are pyrogenic exotoxins
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What percentage of strains of strep pyogenes produce pyrogenic exotoxins?
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20-25%
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How do superantigens work?
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They bind to the outside of the T cell-MHC complex leading to the activation of nearly all T cells
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What are some examples of exo-enzymes secreted by strep pyogenes?
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hyaluronidase, streptokinase, C5a peptidase
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How is strep pyogenes transmitted?
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through respiratory droplets and exchanging secretions
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What are the most likely places strep pyogenes would be found?
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In the upper respiratory tract and transiently on the skin; it is NOT CONSIDERED NORMAL FLORA
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What group of people is most likely to become infected with strep pyogenes and where is the infection?
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Children 5-15 get URT and skin infections as well as people with chronic illnesses, elderly, and immunosuppressed
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What sort of respiratory infections can be caused by strep pyogenes?
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Pharyngitis, scarlet fever, and pneumonia
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What is scarlet fever?
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Scarlet fever is strep throat complicated by the production of pyrogenic exotoxin causing a characteristic rash; it is a LOCAL infection with a SYSTEMIC toxemia
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What is acute rheumatic fever?
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An inflammatory reaction that is seen ONLY after an infection with a strep pyogenes pharyngitis; seen mostly in children
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What are the symptoms of rheumatic fever?
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carditis, arthritis, erythematous skin lesions
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What is the likely pathogenesis of rheumatic fever?
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hyperimmune response to strepococcal antigens that cross-react with host tissue such as the heart valves
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What is acute glomerulonephritis?
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Kidney inflammation seen after a prior pharyngitis or skin infection with strep pyogenes
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What is the pathogenesis of post streptococcal glomerulonephritis?
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Deposition of immune complexes in the basement membrane of the glomerulus
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What is PANDAS?
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Pediatric autoimmune neuropsychiatric disorder associated with group A beta-hemolytic strep; shows OCD symptoms following a GAS infection
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What is used to treat strep pyogenes?
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Initially treated with penicillin, but invasive disease is treated with clindamycin or erythromycin
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