Mycoplasmas belong to the family Mollicutes, which includes Acholeplasma, Ureaplasma and other species. However the term "Mycoplasma" is most often used as a "cover-all". More than 180 species have been identified of which 20 distinct Mycoplasma and Acholeplasma species from human, bovine and swine have been isolated from cell culture. There are 6 species that account for 95% of all mycoplasma infections (M.orale, M.arginii, M.fermentans, M.salivarum, M.hyorhinis and A.laidlawii). Mycoplasmas are widespread in nature as parasites of humans, mammals, reptiles, insects and plants. They are the smallest and simplest self-replicating prokaryotes, they lack a rigid cell wall and are surrounded by a single plasma membrane. They are dependent on their hosts for many nutrients as their biosynthetic capabilities are limited.