Rhodococcus equi

Lisa A. Spacek, M.D., Ph.D.

MICROBIOLOGY

  • Pleomorphic Gram-positive coryneform aerobic bacteria. Non-spore-forming, non-motile, non-fermenting, and weakly acid-fast on Ziehl-Neelsen smear.
    • Appears coccoid in solid media and pleomorphic in liquid media.
    • May be mistaken as "diphtheroid" contaminant or a Mycobacterium.
  • Grows well on ordinary media, named "rhodo" (red) for salmon color. Mucoid coalescing colonies seen after 4 days growth on solid media.
  • Soil inhabitant; infection via inhalation, inoculation or ingestion
    • Recognized equine pathogen, foals serve as reservoir and develop pyogranulomatous pneumonia.
  • R. equi is an intracellular pathogen and enters the phagosomes of macrophages.[2]
    • Virulence plasmids are associated with human, equine, porcine, and caprine (goats) isolates.[1]

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