Mycoplasmas are bacteria that lack a cell wall, are small in size, and have the smallest genome among all independently replicating forms of life .Because of their small genome and the lack of many metabolic pathways, they are fastidious microorganisms. For isolation, they have complex nutritional requirements but will grow on specialized artificial medium containing serum. Growth in broth and on agar media is slow (5–21 days), and the small (0.1–1 mm diameter) colony morphology typically has a "fried egg" appearance under low magnification. Mycoplasmas do not survive for more than a few days outside the host and are vulnerable to common disinfectants.
More than 20 Mycoplasma species have been isolated from avian hosts; However, only 4 species are considered pathogenic in poultry. M gallisepticum and M synoviae are pathogenic for chicken, turkey, and other species, and M meleagridis and M iowae are pathogenic primarily in turkeys. M meleagridis has been eradicated from commercial turkeys, but the other 3 species still have economic importance. Each of these has distinctive epidemiologic and pathologic characteristics.