Category:Corynebacterium species

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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. 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

Corynebacterium renale

Corynebacterium bovis

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