Mycobacterium in the context of "Actinomycetota"

Mycobacteriaceae is a family of bacteria in the phylum Actinomycetota. Its name is derived from the Mycobacterium genus, which includes pathogens known to cause serious diseases in mammals, including tuberculosis (M. tuberculosis) and leprosy (M. leprae) in humans. The Greek prefix myco- means 'fungus', alluding to the mold-like appearance of these organisms on agar plates.

The Ziehl–Neelsen stain, also known as the acid-fast stain, is a bacteriological staining technique used in cytopathology and microbiology to identify acid-fast bacteria under microscopy, particularly members of the Mycobacterium genus. This staining method was initially introduced by Paul Ehrlich (1854–1915) and subsequently modified by the German bacteriologists Franz Ziehl (1859–1926) and Friedrich Neelsen (1854–1898) during the late 19th century.

The acid-fast staining method, in conjunction with auramine phenol staining, serves as the standard diagnostic tool and is widely accessible for rapidly diagnosing tuberculosis (caused by Mycobacterium tuberculosis) and other diseases caused by atypical mycobacteria, such as leprosy (caused by Mycobacterium leprae) and Mycobacterium avium-intracellulare infection (caused by Mycobacterium avium complex) in samples like sputum, gastric washing fluid, and bronchoalveolar lavage fluid. These acid-fast bacteria possess a waxy lipid-rich outer layer that contains high concentrations of mycolic acid, rendering them resistant to conventional staining techniques like the Gram stain.

Auramine O is a diarylmethane dye used as a fluorescent stain. In its pure form, Auramine O appears as yellow needle crystals. It is insoluble in water and soluble in ethanol and DMSO.

Auramine O can be used to stain acid-fast bacteria (e.g. Mycobacterium, where it binds to the mycolic acid in its cell wall) in a way similar to Ziehl–Neelsen stain. It can also be used as a fluorescent version of the Schiff reagent.

The Actinomycetota (previously known as "Actinobacteria") are a diverse phylum of Gram-positive bacteria with high GC content. They can be terrestrial or aquatic. They are of great importance to land flora because of their contributions to soil systems. In soil, they help decompose organic matter of dead organisms so the molecules can be taken up anew by plants. While this role is also played by fungi, actinomycetota are much smaller and likely do not occupy the same ecological niche. In this role, the colonies often grow extensive mycelia, as fungi do, and the name of an important order of the phylum, Actinomycetales (the actinomycetes), reflects that they were long believed to be fungi. Some soil actinomycetota (such as Frankia) live symbiotically with the plants whose roots pervade the soil, fixing nitrogen for the plants in exchange for access to some of the plant's saccharides. Other species, such as many members of the genus Mycobacterium, are important pathogens.

Beyond the great interest in Actinomycetota for their soil role, much is yet to be learned about them. Although currently understood primarily as soil bacteria, they might be more abundant in fresh waters. Actinomycetota is one of the dominant bacterial phyla and contains one of the largest of bacterial genera: Streptomyces. Streptomyces and other actinomycetota are major contributors to biological buffering of soils. They are also the source of many antibiotics.

Mycobacterium ulcerans is a species of bacteria found in various aquatic environments. The bacteria can infect humans and some other animals, causing persistent open wounds called Buruli ulcer. M. ulcerans is closely related to Mycobacterium marinum, from which it evolved around one million years ago, and more distantly to the mycobacteria which cause tuberculosis and leprosy.