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33 Cards in this Set

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besides diphtheria, what can cornebacterium diphtheria cause?
charac of Corynebacteria genus
G+ (pleomorphic)
coryneform (club shaped)
normally harmless; inhabit nasopharynx, URT, GI, skin (except C. diphtheria)
virulence factors for C. diphtheria
Diphtheria toxin (DT)
charac of the diphtheria toxin (DT)
AB exotoxin
inhibit protein syn
encoded on lysongenized bacteriophage
how is DT regulated?
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
what is the DT receptor? where does DT do its damage and how?
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
pathogenesis of diphtheria
can be carried for months after infection
asx carriers
unvaccinated hosts
respiratory spread
clinical disease for respiratory diphtheria
2-6 days incubation
intial damage due to exotoxin; prod pseudomembrane
self-resolving ~1 week
what is pathognomic for diphtheria?
pseudomembrane- tough, fibrous exudate
filled with PMNs, necrotic spithelial cells, RBCs, bacteria
covers tonsils, uvula, palate
what is one major way to distinguish between strep pyogenes and c. diphtheria?
type of exudate
s. pyogenes: tonsillar, milky white
diphtheria: pseudomembrane
how does the exotoxin (DT)enter the system and spread?
absorbed through mucosa; carried through circulation
what are some other ex of diphtheria infections (not respiratory)?
nasal diphtheria (mild, chronic)
cutaneous diphtheria (via contact; more common than resp; chronic ulcer)
complications of diphtheria
obstructed breathing
cardiac arrhythmias
neuritis, peripheral neuropathy, motor paralysis
death (10-30%)
signs of diphtheria
gross swelling, congestion of pharyngeal, tonsillar area
"dirty white" exudate
"Bull neck"- perglandular edema (cheek to neck)
what type of lab diagnosis us unreliable for diphtheria and why?
microscopy- FN AND FP
many normal flora look similar; some diphtheria dont produce exotoxin
lab diagnosis of c. diphtheria
culture and Elek test (for toxin)
selective medium (potassium tellurite medium)- inhibits growth norm flora
corynebacteria prod gray/black colonies
what is the test for DT?
Elek test: immunodiffusion assay based on IC formation at equivalence pt
precipitation indicates presence of toxin
what is the treatment for diphtheria?
antitoxin admin early (passive)
penicillin, erythromycin
respiratory support
preventing diphtheria
DPT (toxoid) vaccine with boosters (b/c whole, inactivated)
contacts to infected should receive boosters (prevents 2ndary spread)
charac of bortedella pertussis
G- coccobacillus
sensitive to drying?
epidemiology of b. pertussis
humans only reservoir
aerosol/direct contact transmission
part of DPT vaccine
still endemic
why is b. pertussis still endemic even with vaccine?
immunity wanes in adults
lack of immunization in children
in addition to b. pertussis what are 2 other causes of whooping cough?
B. parapertussis
B. bronchiseptica
virulence factors for B. pertussis
ADHESINS: FHA (filamentous hemagglutination), pertactin, pertussis toxin
also, tracheal cytotoxin
what do FHA and pertactin bind?
contain RGD sequences to bind integrins on host cells
what is the mxn for pertussis toxin?
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
what is the mxn of the tracheal cytotoxin from b. pertussis?
subunit of PG
inhibit DNA syn
kills ciliated cells in resp
incr IL-1 (fever)
pathogenesis of whooping cough
paroxysmal cough
clinical disease in whooping cough
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)
lab diagnosis of b. pertussis
microscopy: FP
culture: CCBA medium (charcoal, cephalexin blood agar; Bordet-Gengou, Regan-Lowe; selective b/c antibiotic inhibits growth norm flora)
describe the serology for diagnosis of B. pertussis
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
tx of pertussis
primarily supportive
<1% req hydration, O2, steroids (babies, elderly)
preventin and control of pertussis
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