Reference Tables

Bacterial Organisms by Morphology/Oxygen Requirement [Equine]

Aerobes/Facultatives Anaerobes
Gram-Positive Cocci

  • Streptococcus spp. (often in chains)
  • Staphylococcus spp.
  • Enterococcus spp.
  • Dematophilus congolensis (“railroad tracks”)

Filamentous, branching rods

  • Actinomyces spp. (may also be anaerobic)


  • Rhodococcus equi
  • Corynebacterium spp. (“diptheroid” appearance)

  • Clostridium spp. (incl. botulinum, tetani, difficile, and perfringens)
  • Actinomyces bovis
Gram-Negative Bacilli (enteric spp.)

  • Escherichia coli
  • Proteus spp.
  • Salmonella spp.
  • Lawsonia intracellularis

Bacilli (non-enteric spp.)

  • Actinobacillus spp.
  • Pasteurella caballi
  • Pseudomonas spp.
  • Brucella abortus
  • Burkholderia mallei
  • Taylorella equigenitalis

  • Fusobacterium spp.
  • Bacteroides fragilis
  • Intracellular: Neorickettsia spp., Anaplasma spp.
  • Spirochetes: Leptospira spp. (G-), Borrelia burgdorferi (G-)
  • Acid fast: Mycobacterium spp.


Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

OSU VMC Antimicrobial Use Guidelines Copyright © 2018 by The Ohio State University College of Veterinary Medicine is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.