Scanning electron micrograph of Actinomyces israelii.
Scientific classification
Kingdom: Bacteria
Phylum: Actinobacteria
Class: Actinobacteria
Subclass: Actinobacteridae
Order: Actinomycetales
Buchanan, 1917

The Actinomycetales are an order of Actinobacteria. They are very diverse and contain a variety of subdivisions, as well as yet-unclassified isolates, mainly because some genera are very difficult to classify because of a highly niche-dependent phenotype. For example, Nocardia contains several phenotypes first believed to be distinct species before their differences were shown to be entirely dependent on their growth conditions.

Difficulty of classification

Actinomycetales are Gram-positive, but several species have complex cell wall structures that make the Gram staining unsuitable (e.g. Mycobacteriaceae).


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