Actinomycetes

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.”

Introduction to Pathogenic Fungi and Superficial Mycoses

Fungi (singular fungus) are eukaryotes. They generally occur in two forms: yeast, which can be round or oval and basically unicellular, but capable of forming long chains called pseudomycelium; and the mold or filamentous. Some pathogenic fungi can be yeast-like inside animal tissue and filamentous in their natural habitat. Also, fungi have a highly developed form of sexual reproduction, but most can also multiply asexually. The natural habitat of a majority of fungi is soil where they perform their primary function in nature, that is, decomposing plant material and recycling the biomass in the ecosystem. However, certain pathogenic fungi are more frequently associated with pigeon or bat excreta. A majority of fungi are harmless to humans and animals. Only a small number of species are known to cause diseases in humans and animals though a majority of plant diseases are caused by fungi. The tissue reaction is usually granulomatous. Fungal infections do not respond to antibacterial antibiotics.