LECTURE - Diphtheriae

Question 1

Corynebacteria characteristics

Answer 1

• gram +
• non-motile
• facultative anaerobic bacilli

Question 2

where are most species of Corynebacteria found?

Answer 2

mucous membranes of humans and animals

some can be found in plants and in the environment (free-living saprophytes)

Question 3

“coryne”

Answer 3

• club

- rod-like organisms appear larger on one end than the other, like a club = coryneforms

Question 4

CMN group of Corynebacteria

Answer 4

• cell walls of corynebacteria have meso-DAP (diamenopimlic acid) + short-chained mycolic acids
• mycolic acids = more resistant to certain chemicals + stimulate immune system (adjuvant)

Question 5

These spp. also have meso-DAP but longer chains of mycolic acid

Answer 5

Mycobacteria and Nocardia

Question 6

This will stain polychromatic granules that accumulate on one end of corynebacteria that gives it its club shape

Answer 6

Albert’s stain

Question 7

To differentiate C. diphtheria from other Corynebacteria using agar plates

Answer 7

will reduce teleria if you add telerium on Tinsdale agar

Question 8

Corynebacterium cell envelope

Answer 8

top layer, mycomembrane with porin, arabinogalactan, peptidoglycan, plasma membrane with lipomannan (LM) and lipoarabinomannan (LAM) that might differ across secies
** also S-layer and pili

Question 9

These bacteriophage genes within C. diphtheriae encode diphtheria toxin

Answer 9

beta or omega

- A-B toxin but a single polypeptide chain

Question 10

where does C. diphtheriae bind

Answer 10

back of throat

Question 11

___ _____ environment allows expression of diphtheria toxin

Answer 11

low iron

Question 12

What happens after expression of diphtheria toxin

Answer 12

• secreted toxin is proteolytically cleaved

- toxin binds heparin-binding epidermal growth factor (HB-EGF) on surface of target cell

Question 13

Diphtheria toxin entry into cell cytosol

Answer 13

1. toxin binds to receptor
2. internalized in clathrin-coated pits into early endosomal vesicles; acidification of endosomal lumen
3. transmembrane domain = spontaneous dynamic reorganization and inserts into membrane forming pore
4. A subunit delivered to cytosol (COPI complex, thioredoxin reductase + Hsp90)
   - refolded into active conformation = A subunit catalyzes ADP-ribosylation of elongation factor 2

Question 14

What makes diphtheria toxin a cytotoxin

Answer 14

EF2 ribosylation will stop cell protein synthesis thus killing it

• A subunit modifies diphthamide on EF2
• same mechanism used by exotoxin A of Pseudomonas aeruginosa

Question 15

leathery and well stuck to the back of throat pseudomembrane

Answer 15

diphtheria toxin

Question 16

T or F. Childhood vaccines can prevent diphtheria

Answer 16

T!
- when infected, not a bad idea to give someone Abs to op up released toxins so can’t cause further damage bc toxins can be released once the organism is lysed

Question 17

non-toxic mutant of DT

Answer 17

CRM197

Question 18

a successful carrier protein in conjugate vaccines

Answer 18

diphtheria toxoid

Question 19

Diagnosing diphtheria

Answer 19

• colonies on Tinsdale or CTBA media producing brown ‘halo’
• gram + rods
• urease neg