Rhodoccocus hoagii


  • This pleomorphic, non-motile Gram-positive coccobacillus [Fig 1] has undergone several name changes.
    • Formerly known as Corynebacterium equi, then Rhodococcus equi, and later on Rhodoccushoagii (due to the realization R. equi had an earlier heterotypic synonym in Corynebacterium hoagii).
  • Ubiquitous in the environment.
  • Variably acid-fast staining.
  • Organism varies from coccoid to bacillary form depending on growth condition.
    • Solid media: coccoid, salmon-pink color colonies [Fig 2] may not appear until 4-7 days after incubation.
    • Liquid media: bacillary, branching [Fig 3].
  • Modes of acquisition: inhalation, local inoculation, or ingestion.
    • A common cause of bronchopneumonia in foals, also swine and cattle.
  • It can be overlooked as contaminant diphtheroids and be discarded.
    • The lab should be aware if clinically suspected.
    • It can also be confused with Micrococcus, Bacillus or Mycobacteria species.

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Last updated: August 8, 2022