Actinomycetes are a group of metabolically dynamic microorganisms. They are better known for the production of a wide range of antibiotics, anticancer drugs, and industrial enzymes. Only a small number of species belonging to the order Actinomycetales are pathogenic. From the evolutionary perspective, actinomycetes form a bridge between the classic bacteria and fungi. The properties that mandate their classification with bacteria include prokaryotic cell structure and in vitro sensitivity to most antibacterial antibiotics. On the other hand, their tendency to form true branching with septate mycelium, external spores, and granulomatous tissue reaction in infected hosts bring them closer to fungi. The term “actinomycete” literally means “ray fungus.” Because of their fungus-like properties, actinomycetes have been traditionally studied by mycologists. By early 1970s, it became obvious that these are prokaryotic microorganisms, and most mycologists started avoiding them, but bacteriologists did not quite embrace them either. As a result the study of actinomycetes has fallen into a “no man’s land.”
