Article Sections

Introduction

Diphtheria is an infectious disease caused by Corynebacterium diphtheriae, a gram-positive bacillus that is transmitted via aerosolized droplets.  C diphtheriae exists in nontoxigenic and toxigenic forms, and the toxigenic form can cause systemic and local symptoms.

Pathogenesis and risk factors

C diphtheriae is a nonmotile, unencapsulated, gram-positive bacillus transmitted via aerosolized droplets (eg, coughing, sneezing).  C diphtheriae colonizes the upper respiratory tract, but local invasion is rare.  Instead, the primary virulence factor is diphtheria toxin, an exotoxin comprising 2 major subunits:

  • B (ie, binding) subunit:  Binds the epidermal growth factor receptor for endocytosis of the toxin.
  • A (ie, active) subunit:  Irreversibly inhibits protein synthesis through ADP ribosylation of elongation factor-2, leading to cell death and the following symptoms:
    • Local tissue damage:  Pharyngitis, laryngotracheitis.

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