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28 Cards in this Set
- Front
- Back
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Streptococci group characteristics
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-GP cocci chains
-fail to produce catalase (in contrast to staph) -grow best on blood agar> can use to determine alpha vs beta hemolysis |
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alpha vs beta hemolysis
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-seen in strep
-B- complete hemolysis, clear around colonies on blood agar -a- hazy, green on blood agar due to incomplete hemolysis |
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3 major groups of streptoccci
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-pyogenic (B-hemolytic, group Ags)
-pneumococci (a-hemolytic, capsule, no group Ags) -Viridans (a hemolytic, no group Ags, no capsule, part of normal oral flora) >>>>>Enterococcus is no longer in this group (has group D Ag) |
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Group A Strep (GAS)
-name the 2 toxins that cause b-hemolysis |
-streptolysin S
-streptolysin O (oxygen stabile) |
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Structures of GAS cell wall
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-M protein (80 diff serotypes)
-F protein -lipotechoic acid -pili |
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M protein
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-on GAS
-on cell wall, extends out and serves as Ag for serotyping (>80 serotypes) -biologic funtion assigend to specific domains such as antigenicity or capacity to binds molecules like fibrinogen, serum factor H, and Igs |
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Streptolysin O (SLO)
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Exotoxin of GAS
-pore forming -causes B-hemolysis -is antigenic and is the basis for the serologic test antistreptolysin O (ASO) |
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StrepSAgs
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-strep super antigens
-made by about 10% GAS -similar to StaphSAg -multiple effects such as fever rash, scarlet fever, T-cell proliferation, B-cell supression -cytokines released through super Ag mechanism |
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Dz caused by GAS
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-pharyngitis
-impetigo -wound and puerperal infections -strep TSS -post strep dz (acute rheumatic fever and rheumatic dz) -poststreptococcal glomerulonephritis |
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Impetigo
-what organism |
GAS
-transient skin colonization with GAS combined with minor trauma, insect bite -spreads locally by scratching and to others by direct contact |
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Streptococcal TSS
-what bug |
GAS
-severe invasive for of GAS soft tissue infection -rapid progression to death -multiorgan involvement> spreads to blood |
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Poststreptococcal sequelae of GAS (2)
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1) ARF (acute rheumatic fever)> does not follow skin or other non-respiratory infections of GAS
-recurrances can be triggered with any GAS infection -injury to heart by common recurrences leads to rheumatic heart disease 2) Poststreptococcal glomerulonephritis> can follow respiratory or cutaneous GAS> involves only certain nephritogenic strains though |
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Acute GAS infection pathogenesis
-nasopharynx vs skin -name 3 adhesins on cell wall surface and function |
-3 adhesins of GAS
-M protein, F protein, LTA (lipotechoic acid) -all 3 involved in nasopharynx infection> attach to fibronectin> M protein provides scaffold for LTA SKIN -M protein binds directly to subcorneal keratinocytes -F protein involves adherence to Ag- presenting langerhans cells |
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How are some GAS resistant to phagocytosis?
-what is the major molecule for this? |
M protein essential
-binds fibrinogen and factor H> diminished alternative pathway -in presence of M specific Ab> classical pathway proceeds |
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Type of HS
-acute rheumatic fever |
Type II
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Type of HS
-Acute glomerulonephritis (post streptococcal) |
Type III
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Acute rheumatic fever follow what infection?
-bug and specific site |
GAS pharyngitis ONLY
(does not follow empitigo) -due to autoantibodies from M protein |
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What type of immunity do you develop to GAS?
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-Ab against M protein is protective BUT only for same M protein (90 diff serotypes)
-called type-specific immunity -IgG to M reverses antiphagocytic properties> Ab bind complement C3b by classical mechanism> phagocyte recognition |
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Streptococcal Pharyngitis
-Clinical, Sx -what age group? -where can it spread? |
-5-15yo
-fever, malaise, headache, sore, red swollen throat, white-yellow exudate -effects uvula, tonsillar pillars, and soft palate -cervical lymph nodes swell -self-limiting SPREADS to: -otitis media, abscesses, suppurative cervical adenitis, acute sinusitis -rarely goes to bacteremia, pneumonia, meningitis |
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Impetigo
-what age? -where on body? |
-usually 2-5 yo
-face and lower extremities -small vesicles surrounded by erythema |
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Erysipelas
-bug -Sx |
caused by GAS
-AFFECTS DERMIS -spreading area of edema and erythema, rapid, well-demarcated edges |
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Scarlet Fever
-3 major charcteristics |
-GAS
-any strains that use StrepSAg -superimposed on pharyngitis 3 characteristics 1) circumoral pallor- cheeks, temples red with pale area around mouth 2) Strawberry tongue- yellow exudate with red papillae 3) Sandpaper rash- appears on second day of illness, spreads from upper chest to trunk then extramities |
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Streptococcal TSS
-Sx -Labs |
GAS
-starts with vague myalgia, chills, and severe pain at infected site (usually skin or soft tissue) leading to necrotizing fascitis and myonecrosis -when it involves extrmities referred to as flesh eating bacteria -continues with nausea vomiting diarrhea> hypotension, shock, organ failure LABS -lymphocytosis -azotemia (impaired renal function) -bacteremia in 50% |
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ARF
-Sx |
GAS
-fever, carditis, subcutaneous nodules, chorea, migratory polyarthritis -cardiac enlargement, murmurs> can lead to heart failure -typically begins 3 weeks after GAS pharyngitis and can last 2-3 months untreated -repeat infections (diff M proteins) lead to progressive heart damage> damage to heart valves, endocardium, scarring, valvular stenosis> called rheumatic heart disease |
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Poststreptococcal Glomerulonephritis
-Sx and timecourse |
GAS
-primarily children -1-4 weeks after pharyngitis -3-6 weeks after skin infection Sx -edema, HTN, hematuria, proteinuria, decreased serum C' |
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Dx GAS
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-Culture- demonstrate B-hemolysis on blood agar
-Serologic grouping identifying group A antigen -Rapid strep test> detect group A Ags directly from throat swab (90% sensitive compared to culture) -High titers of antistreptlysin O (ASO) are usually found in pts with rheumatic fever |
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Rx GAS
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-susceptible to Penicillin G> resistance unknown> drug of choice
-treatment may not prevent glomerulonephritis |
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Prevention of GAS
-what scenarios would you use phylaxis? |
-penicillin prophylaxis is used to prevent recurrences of ARF during susceptible years (5-15yo)
-people with Hx of ARF use penn prophylaxis if undergoing dental extraction> can lead to bacteremia |
