15 plus species including:


Actinobacillus actinomycetemcomitans
Actinobacillus capsulatus
Actinobacillus equuli Actinobacillus hominis Actinobacillus lignieresii Actinobacillus muris Actinobacillus pleuropneumoniae Actinobacillus rossii Actinobacillus seminis Actinobacillus suis Actinobacillus (Pasteurella) ureae


Gram Stain: Negative. The organism exhibits irregular staining.
Morphology: Spherical, oval, and rod shaped. The cells are mostly bacillary but are interspersed with coccal elements which often lie at the pole of a bacillus giving a characteristic "Morse code" form. The cells are arranged singly, in pairs, or more rarely in chains.
Size: 0.3 - 0.5 micrometers by 0.6 - 1.4 micrometers.
Motility: Non-motile.
Capsules: No.
Spores: No.


Colonies are small, sticky and adherent to the agar surface. Most species are non-hemolytic on blood agar, however colonies of Actinobacillus suis on sheep blood agar is always surrounded by a clearly marked zone of hemolysis. Colonies of this genus are non-pigmented. Surface cultures have a low viability and die in 5 to 7 days.


Respiratory and fermentative; complex nutrients needed; no gas from the fermentation of glucose, lactose, etc.



Commensal organisms of the respiratory, alimentary and genital tracts of humans and animals, pathogenic if introduced into tissue.


Most members of the genus are found both as pathogens and as commensal organisms in domestic animals. Occasionally, they may be found associated with disease in man, and one species ( Actinobacillus actinomycetemcomitans ) occurs, with only isolated exceptions, in man alone. The diseases caused by actinobacilli are usually of a sporadic nature, but occasionally a group of animals may be affected when a common "trigger" factor is present. For example, A. lignieresii is pathogenic for both cattle and sheep and A. equuli is pathogenic for horses and pigs, causing purulent nephritis and arthritis especially in foals and piglets. Actinobacilli are opportunistic pathogens and translation from a commensal to a pathogenic organism usually involves some factor which assists in the entry and establishment within tissues.


For culture: Columbia Blood Agar, Blood Agar 5%.
For selective isolation: MacConkey Agar.
For maintenance: Blood Agar 5% or Cooked Meat Media.


Temperature: Optimum temperature for growth 35 degrees C.
Time: 48 - 72 hours.
Atmosphere: 5 - 10% CO 2.


1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams & Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology , Volumes I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.

4. Murray, P.R., et al. 1995. Manual of Clinical Microbiology , 6th ed. American Society for Microbiology, Washington, D.C.

5. Internet: /Bacterial Database Search, February, 1998.