C. diphtheriae Flashcards
What are the four characteristic symptoms of diphtheria?
- Bull neck - big neck from severe swelling of the cervical lymph nodes and mucosa
- Pseudomembrane on the uvula, tongue and soft palette - results from wbc, rbc and fibrin deposition, can block throat
- Skin lesions
- Myocarditis, neuritis
What three tests are used to identify Corynebacterium diphtheriae?
- Albert’s stain
- Confirmatory culture
- Elek’s test
What does an alberts stain entail?
- Albert’s A - toluidine blue, malachite green, glacial acetic acid, alcohol
- Albert’s B - iodine and potassium iodine in water
- Stains metachromic (volutin) granules
What does a confirmatory cullture entail?
Tinsdale agar contains tellurite with is reduced by diptheriae, causing black precipitates.
What does an Elek’s test entail?
Looks for antigen-antibody precipitate on agar - positive control, negative control, and experimental
What is a metachromic granule?
Stores phosphate in diphtheriae, high energy compound
In what strains is DTX produced?
Strains lysogenized with the beta phage
What gene encodes DTX, and what is it regulated by?
tox gene, regulated by DtxR in response to iron
What does the A subunit of DTX entail?
- ADP ribosyltransferase catalyzes ADP-ribosylation of EF-2
- Uses NAD+ as a cofactor
- ADP-ribose is attached at a derivative of histidine called diphthamide
- Inhibits protein synthesis and kills target host cell
What does the B subunit of DTX entail?
- Binds to heparin-binding EGF-like growth factor (HB-EGF) receptor in humans and monkeys (not in rodents)
- CD9 copurifies with HB-EGF and increases affinity of DTX for HB-EGF receptor
What is the mode of action of DTX?
five steps
- B domain binds to host membrane bis HB-EGF receptor
- Enters via endocytosis (receptor mediated)
- A is cleaved but attached to B subunit by disulfide bonds, which are reduced in acidic endosome
- Transmembrane domain facilitates passge of the A peptide through the vesical membrane (endosomal escape)
- A domain ADP-ribosylates elongation factor 2 (EF-2), halts prtein synthesis and kills the cell
How is diptheria prevented and treated?
Prevented through immunization with formalin-inactivated DTX - administered with tetanus toxoid
Treated with antibiotic therapy - isolated for 48hrs, erythromycin and penicillin G
Antitoxin is produced in horses and neutralizes unbound toxin
Who was Jim the Horse?
A horse who contracted tetanus and was euthanized - DTX antitoxin was retrieved and given to children, some of which contracted tetanus as well and died
