RANK: Genus

TAXONOMY: cellular organisms -> Bacteria -> Proteobacteria -> Gammaproteobacteria -> Pasteurellales -> Pasteurellaceae -> Actinobacillus


'Actinobacillus' is a genus of Gram-negative, immotile and nonspore-forming, oval to rod-shaped bacteria occurring as parasites or pathogens in mammals, birds, and reptiles. It is a member of the Pasteurellaceae family. The bacteria are facultatively aerobic or anaerobic, capable of fermenting carbohydrates (without production of gas), and of reducing nitrates. The genomic DNA contains between 40 and 47 mol % guanine plus cytosine. Actinobacillus (Pasteurella) ureae and A. hominis occur in the respiratory tracts of healthy humans and may be involved in the pathogenesis of sinusitis, bronchopneumonia, and meningitis. A. actinomycetemcomitans occurs in the human oral microflora, and together with anaerobic or capnophilic organisms (HACEK group organisms) may cause endocarditis. Actinobacilli are susceptible to most antibiotics of the beta-lactam family, aminoglycosides, tetracyclines, chloramphenicol, and many other antibacterial chemotherapeutics. An analysis of A. actinomycetemcomitans indicated it was monophyletic with Haemophilus aphrophilus and H. segnis, and it was proposed that they be reclassified as a new genus, Aggregatibacter (from the Latin, 'aggregare', meaning 'to come together'). 

Cells, measuring 0.4 ± 0.1 × 1.0 ± 0.4 µm, are spherical, oval, or rod-shaped (Phillips, 1984). Most often bacillary but sometimes interspersed with coccal elements that may lie at the pole of a larger form, producing the characteristic “Morse-code” form. Cell forms up to 6 µm in length may appear when grown on media containing glucose or maltose. Cells are single or arranged in pairs or, more rarely, in chains. Endospores are not formed. Gram negative, but staining is irregular. Not acid fast. India ink may demonstrate small amounts of extracellular slime in wet preparations. Nonmotile. Organisms are aerobic, microaerobic, facultatively anaerobic, or chemoorganotrophic, having both respiratory and fermentative types of metabolism. After growth for 24 h on blood agar, translucent colonies, usually 1–2 mm in diameter appear. Surface colonies have low viability and may die in 2–7 days. Growth may be very sticky upon primary cultivation, making it difficult to remove colonies completely from the agar surface. Optimum growth temperature is 37°C. Temperature range for growth is 25–42°C.

The mol% G + C of the DNA is: 35.5–46.9.

Type species: Actinobacillus lignieresii

This genus contains microbial species that can reside in the human gastrointestinal tract. [PMC 4262072]

Gut associated
Microbial Abundance Data: Actinobacillus
Percent of total population with standard deviation [PMID: 22698087]. Percentages > 1% highlighted.
0.833 %
1.854 %
0.637 %
0.461 %
0.278 %
0.644 %
0.001 %