Corynebacterium diphtheriae

Question 1

Physical description of C. diphtheriae

Answer 1

• Gram positive
• club shaped
• pleomorphic
• aerobic rod
• has OM with mycolic acid

Question 2

Visualization of C. diphtheriae

Answer 2

• reduce potassium tellurite to tellurium metal

- black precipitate on tellurite blood agar

Question 3

Clinical presentation of C. diphtheriae

Answer 3

• initial throat infection with sore throat, fever, swollen lymph nodes
• bull neck
• pseudomembrane; forms at back of throat, may obstruct airway, la garrotilla

Question 4

Clinical presentation of C. diphtheria due to toxins

Answer 4

• toxin absorbed in blood, affects the liver, heart, kidneys
• toxigenic strains identified by Elek immunodiffusion test
• filter paper with antitoxin placed at right angles to streaks of the strains
• toxin and antitoxin form precipitate

Question 5

Epidemiology of C. diphtheria

Answer 5

• spread via aerosolized droplets
• usually childhood disease
• adults used to be immune, now less due to lack of exposure and poor booster immunizations
• mortality rate fairly high

Question 6

Pathogenesis of C. diphtheria

Answer 6

• AB toxin from beta phage conversion
• B binds to EGF like receptor and internalized
• low pH of phagocytic vesicle allows partial denaturing of toxin and hydrolysis
• A binds NAD and ADP ribosylates EF2, thereby stopping protein synthesis

Question 7

Pathogenesis of C. diphtheria

Answer 7

• tox genes controlled by DtxR repressor, Fe is a corepressor
• toxAB operon off at Fe, maximal production at 2um
• Fe is normally kept low in the body by siderophores like lactoferrin/transferrin

Question 8

Control of C. diphtheria

Answer 8

• passive immunity to neonate
• formalin treated toxoid vaccine(DTap, DPT) for children
• booster(Tdap) before school

Question 9

Control of C. diphtheria once infected

Answer 9

• quarantine
• equine antitoxin in large doses
• penicillin/erythromycin to keep numbers of bacteria low
• but it is an intoxication, not an infection