Ac.ti.no.ba.cil'lus. Gr. fem. n. actis a ray; L. dim. masc. n. bacillus a small staff or rod; N.L. masc. n. Actinobacillus ray bacillus or rod.

Proteobacteria / Gammaproteobacteria / Pasteurellales / Pasteurellaceae / Actinobacillus

Actinobacillus is a genus within the family Pasteurellaceae. The sensu stricto definition of the genus Actinobacillus has been adopted for this Manual, meaning the genus comprises 10 species – Actinobacillus anseriformium, Actinobacillus arthritidis, Actinobacillus capsulatus, Actinobacillus equuli, Actinobacillus hominis, Actinobacillus lignieresii, Actinobacillus pleuropneumoniae, Actinobacillus suis, Actinobacillus ureae, and Actinobacillus vicugnae. Members of the genus Actinobacillus are Gram-negative, facultatively anaerobic, and nonmotile cells that are coccoidal or rod shaped. 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. Members of the genus are not acid fast. Isolates can have 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. The optimum growth temperature is 37°C. The temperature range for growth is 25–42°C. Several species are regarded as primary pathogens of animals, while the remaining species are typically normal flora of the mucosal surfaces of the respiratory or genital tract of humans or animals with some potential to play a secondary role in disease processes under some conditions.

DNA G + C content (mol%): 39.9–41.3 (WGS).

Type species: Actinobacillus lignieresii Brumpt 1910^AL.