MICROBIOLOGY

• 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.