Corynebacterium

• Corynebacteria


  A large diverse group of bacteria, mostly normal flora of skin and mucous membranes of humans and animals
• Corynebacterium diphtheriae

  • Main pathogen causing diphtheria
  • Gram-positive rods
  • Slightly curved, "club shaped" or coryneform
• C. diphtheriae is carried in the upper respiratory tract and spread by droplet infection or hand-to-mouth contact
• Incubation period for C. diphtheriae is 2-5 days
• Diphtheria toxin

  An exotoxin that is the major virulence factor
• Commonest site of infection

  • Tonsils or pharynx
• Host response to C. diphtheriae

  1. Local inflammation

  2. Antibody neutralization of exotoxin
• Local inflammation

  • Fibrinous exudate forms tough, adherent, gray pseudomembrane
• Antibody neutralization

  • Blocks interaction of binding domain with receptors
  • Prevents entry into the cell
• Respiratory diphtheria

  • Illness begins gradually
  • Characterized by low-grade fever, malaise, and mild sore throat
  • Pseudomembrane may spread downward
  • Potential for suffocation
  • Systemic effects involving kidneys, heart, and nervous system
  • Demyelinating peripheral neuritis can result in paralysis
  • Death often results from cardiac failure
• Cutaneous diphtheria

  • Nonhealing ulcers with a dirty gray membrane
  • Systemic complications are less common than from upper respiratory infections
• Laboratory diagnosis

  1. Isolating the organism

  2. Demonstrating toxin production
• Throat swab culture

  • Loeffler's medium
  • Tellurite plate
  • Blood agar plate
• Diagnostic criterion

  • Typical gray-black color of tellurium in the colony
• C. diphtheriae microscopy

  • Highly pleomorphic gram-positive bacillus
  • Appears in palisades or as individual cells in "V" and "L" formations
• Staining characteristics


  • Stains irregularly
  • Gives a beaded appearance
  • Metachromatic granules represent accumulation of polymerized polyphosphates
• C. diphtheriae culture

  • Facultative anaerobe
  • Grows best on blood or serum medium
  • Cystine-tellurite blood agar is selective and differential
• Tests for toxigenicity

  1. Demonstrating that the isolate produces diphtheria toxin

  2. Elek's immunodiffusion test

  3. ELISA

  4. PCR
• Schick's test

  1. Intradermal injection of purified standardized toxin

  2. Inflammation at the site indicates no antitoxin

  3. No inflammation indicates presence of antitoxin and immunity
• Treatment of diphtheria

  • Prompt administration of antitoxin
  • Antimicrobial agents eliminate focus of infection
  • Drug of choice is penicillin (or erythromycin in penicillin hypersensitivity)
• Prevention of diphtheria

  • Immunization with diphtheria toxoid
  • Usually given as a combination vaccine with tetanus toxoid and pertussis vaccine
• Other Corynebacteria

  • Corynebacterium amycolatum
  • Corynebacterium jeikeium
  • Corynebacterium pseudodiphtheriticum
  • Corynebacterium ulcerans
  • Corynebacterium urealyticum
• Corynebacterium amycolatum


  • Prosthetic joint infection
  • Bloodstream infection
  • Endocarditis
• Corynebacterium jeikeium

  • Prosthetic infections
• Corynebacterium pseudodiphtheriticum

  • Respiratory infections
• Corynebacterium ulcerans

  • Skin ulcers
  • Exudative pharyngitis
• Corynebacterium urealyticum


  • UTIs