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33 Cards in this Set
- Front
- Back
besides diphtheria, what can cornebacterium diphtheria cause?
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pharyngitis
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charac of Corynebacteria genus
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G+ (pleomorphic)
coryneform (club shaped) NO SPORES aerobic normally harmless; inhabit nasopharynx, URT, GI, skin (except C. diphtheria) |
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virulence factors for C. diphtheria
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Diphtheria toxin (DT)
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charac of the diphtheria toxin (DT)
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AB exotoxin
inhibit protein syn encoded on lysongenized bacteriophage regulated |
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how is DT regulated?
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DTxR (iron dependent repressor); encoded on chromosome
low iron levels, DTxR inactive, DT gene active high iron levels bind DTxR-> active, DT gene NOT active |
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what is the DT receptor? where does DT do its damage and how?
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receptor: HB-EGF (heparin-binding epidermal GF)
DT must enter to cell to inhibit protein syn in cytoplasm DT binds R (B portion), endocytosed -> endosome, Furin cleaves B subunit; A subunit is translocated to cytoplasm |
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pathogenesis of diphtheria
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can be carried for months after infection
asx carriers unvaccinated hosts respiratory spread |
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clinical disease for respiratory diphtheria
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2-6 days incubation
intial damage due to exotoxin; prod pseudomembrane self-resolving ~1 week |
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what is pathognomic for diphtheria?
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pseudomembrane- tough, fibrous exudate
filled with PMNs, necrotic spithelial cells, RBCs, bacteria covers tonsils, uvula, palate |
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what is one major way to distinguish between strep pyogenes and c. diphtheria?
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type of exudate
s. pyogenes: tonsillar, milky white diphtheria: pseudomembrane |
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how does the exotoxin (DT)enter the system and spread?
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absorbed through mucosa; carried through circulation
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what are some other ex of diphtheria infections (not respiratory)?
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nasal diphtheria (mild, chronic)
cutaneous diphtheria (via contact; more common than resp; chronic ulcer) |
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complications of diphtheria
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obstructed breathing
cardiac arrhythmias myocarditis neuritis, peripheral neuropathy, motor paralysis coma death (10-30%) |
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signs of diphtheria
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gross swelling, congestion of pharyngeal, tonsillar area
"dirty white" exudate "Bull neck"- perglandular edema (cheek to neck) |
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what type of lab diagnosis us unreliable for diphtheria and why?
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microscopy- FN AND FP
many normal flora look similar; some diphtheria dont produce exotoxin |
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lab diagnosis of c. diphtheria
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culture and Elek test (for toxin)
selective medium (potassium tellurite medium)- inhibits growth norm flora corynebacteria prod gray/black colonies |
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what is the test for DT?
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Elek test: immunodiffusion assay based on IC formation at equivalence pt
precipitation indicates presence of toxin |
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what is the treatment for diphtheria?
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antitoxin admin early (passive)
penicillin, erythromycin respiratory support |
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preventing diphtheria
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DPT (toxoid) vaccine with boosters (b/c whole, inactivated)
contacts to infected should receive boosters (prevents 2ndary spread) |
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charac of bortedella pertussis
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G- coccobacillus
sensitive to drying? |
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epidemiology of b. pertussis
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humans only reservoir
aerosol/direct contact transmission part of DPT vaccine still endemic |
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why is b. pertussis still endemic even with vaccine?
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immunity wanes in adults
lack of immunization in children |
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in addition to b. pertussis what are 2 other causes of whooping cough?
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B. parapertussis
B. bronchiseptica (minor) |
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virulence factors for B. pertussis
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ADHESINS: FHA (filamentous hemagglutination), pertactin, pertussis toxin
also, tracheal cytotoxin |
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what do FHA and pertactin bind?
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contain RGD sequences to bind integrins on host cells
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what is the mxn for pertussis toxin?
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AB toxin
heat labile A (S1) unit: ADP ribosyl transferase; activated in host mbr; transfers ADP to Gi subunit turning it off-> no inhibition of adenylate cyclase-> too much cAMP |
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what is the mxn of the tracheal cytotoxin from b. pertussis?
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subunit of PG
inhibit DNA syn kills ciliated cells in resp incr IL-1 (fever) |
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pathogenesis of whooping cough
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paroxysmal cough
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clinical disease in whooping cough
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7-10 day incubation
3 stages: 1. catarrhal (1-2 weeks): very contagious b/c presents as common cold (rhinorrhea, sneezing, low fever) 2. paroxysmal (2-4 weeks):ciliated epithelium destroyed, impaired mucus drainage, "whoop" on inspiration, leukocytosis 3. convalescent: may have 2ndary complications (pneumonia, seizures, encephalopathy) |
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lab diagnosis of b. pertussis
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microscopy: FP
culture: CCBA medium (charcoal, cephalexin blood agar; Bordet-Gengou, Regan-Lowe; selective b/c antibiotic inhibits growth norm flora) serology |
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describe the serology for diagnosis of B. pertussis
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antiserum agglutination
depends on titers of Ig against pertussis toxin and Hemagglutinin req 2 titers (acute and convalescent serum)- must have 4x increase in Ig to the toxin to say it is responsible for disease compare serial dilutions for acute and convalescent |
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tx of pertussis
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primarily supportive
<1% req hydration, O2, steroids (babies, elderly) |
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preventin and control of pertussis
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DPT- whole inactivated
DaPT- multivalent acellular (uses virulence factors; adhesins); less side effects erythromycin prophylaxis to contacts or young kids to prevent relapsel; admin in catarrhal stage may lessen duration/severity |