- Exotoxin - necrotising and neurotoxic effectso fragment A - (action, activity) ® inhibition of protein synthesiso fragment B - (binding) i) ® entry of the toxin into the cell through receptor-mediated endocytosisTheir role in the pathogenesis of infections:- C.diphtheriae typically is not invasive (does not invade deep tissues and does not enter the bloodstream- Transmission - by air droplets or contact with respiratory secretions or contaminated skin abrasions of a symptomatic infected person- C.diphtheriae colonises mucosa or skin- Toxigenic strains (temperate bacteriophage infects C.diphtheriae) produce exotoxin with necrotising and neurotoxic effects ® Destruction of epithelium, superficial inflammation response- Grayish pseudomembrane- Regional lymph nodes in the neck enlarge, and marked oedema of the entire neck may be present- Distant toxic systemic damage (parenchymatous degeneration, fatty infiltration, necrosis) affectingo heart muscle (myocarditis)o livero kidneys (tubular necrosis)o adrenal glandso nerves (demyelination → resulting in paralysis of the soft palate, eye muscles, or extremities)- Wound or skin diphtheria Primary (pustule→ulcer covered by a pseudomembrane)- Respiratory diphtheria (Sore throat, low-grade fever- Cutaneous diphtheria (May involve any area of the skin (usually the legs)

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