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Overview

  • Common inhabitants of skin and mucous membranes of animals
  • Opportunistic infections
  • Cause pyogenic infections
  • Most species host specific


Characteristics

  • Small, tough, Gram positive rods
  • Pleomorphic
  • Cluster together to resemble Chinese characters - coryneform morphology
  • Known as diphtheroids
  • Catalase positive, oxidase negative
  • Facultative anaerobes
  • Require enriched media for growth
  • Non-motile


Pathogenesis and pathogenicity

  • Pyogenic causing suppurative infections except for C. bovis
  • C. bovis causes mild neutrophil response in teat canal of healthy dairy cows and may protect from more pathogenic bacteria
  • C. pseudotuberculosis:
    • Facultative intracellular pathogen inside macrophages
    • Cell wall lipid
    • Produces a phospholipase toxin which hydolyses sphingomyelin in mammalian cell membranes
    • Phospholipase may enhance survival and multiplication in host in early stages
  • C. renale
    • Urinary tract pathogens
    • Produce urease and hydrolyse urea
    • Possess fimbriae for attachment to urogenital mucosa
    • Infection when immunity reduced or following tissue damage during parturition


Corynebacterium pseudotuberculosis

  • Caseous lymphadenitis:
    • C. pseudotuberculosis carried on skin of sheep
    • Infection follows tissue trauma such as shearing wounds
    • Incubation period 3 months
    • Chronic suppurative infection of sheep, goats and occasionally cattle
    • Abscessation of superficial and internal lymph nodes if haemtogenous spread occurs
    • Caseous abscesses with green colour and onion ring appearance
    • Ill thrift and pneumonia may occur
    • Condemnation of carcasses and hides
    • Infection spread by pus from abscesses, and oculonasal secretions
    • Organism survives in environment for several months
    • Sandwich ELISA detects circulating antibodies to phospholipase toxin
    • Control: importation measures including screening; culling of infected sheep, stict hygiene; inactivated vaccine
  • Ulcerative lymphangitis in horses:


Diagnosis

  • Samples include pus, exudate, affected tissues and urine
  • Presence of coryneform organisms in smears
  • Culture on blood agar, selective blood agar and MacConkey agar
  • Do not grow on MacConkey
  • Colony characteristics:
    • C. bovis: lipophilic bacterium; small, white, dry, non-haemolytic colonies on plates inoculated with bovine milk
    • C. kutscheri: white colonies; occasionally haemolytic
    • C. pseudotuberculosis: small, white coloniess surrounded by narrow zone of complete haemolysis; colonies become dry and cream-coloured
    • C. renale: small, non-haemolytic colonies after 24 hours; pigment produced after 48 hours
  • Biochemical reactions:
    • Certain strains of C. pseudotuberculosis reduce nitrates
    • All pathogenic strains except C. bovis produce urease
  • Enhancement of haemolysis produced by C. pseudotuberculosis when inoculated across a streak of Rhodococcus equi