Actinomyces israeli is the most common Actinomyces causinghuman infection. Other species are Actinomyces gerencsonei, Actinomyces turicensis, Actinomyces radingae, Actinomyces europaeus, Actinomyces naeslundii, Actinomyces odontolyticus, Actinomyces viscosus, Actinomyces meyeri, and Propionibacterium propionicum.
Actinomyces show the following features:
· Actinomyces organisms are Gram-positive, nonmotile, non-sporing, and non–acid-fast bacilli.
· They measure 0.5–1 mm in diameter.
· They often grow in filaments that separate into bacillary and coccoid filaments.
Actinomyces organisms are facultative anaerobes. They growbetter under anaerobic or microaerophilic conditions at an optimum temperature of 35–37°C. Presence of 5–10% CO2facilitates the growth. Actinomyces species grow slowly; they need a longer incubation period of 3–4 days. A. israeli may require even 7–14 days for growth.
1. Brain heart infusion agar: Brain heart infusion (BHI) agaror heart infusion agar supplemented with 5% defibrinated rabbit, sheep, or horse blood is the enriched medium used frequently for Actinomyces. On these media, in anaerobic to microaerophilic conditions, the bacteria form colonies with a characteristic molar-tooth appearance.
2. Liquid media: Heart infusion blood and thioglycollateblood supplemented with 0.1–0.2% sterile rabbit serum are the examples of liquid media used for culture of Actinomycesspecies.