Mollicutes - History of The Classification

History of The Classification

The classification of the Mollicutes has always been difficult. The individuals are tiny and, being parasites, they have to be cultivated on special media. Until now many species could not be isolated at all. In the beginning it was not clear whether they were fungi, viruses or bacteria. Also the resemblance to L-forms was confusing.

At first all members of the class Mollicutes were generally named "mycoplasma" or "PleuroPneumonia-Like Organism" (PPLO). Mollicutes other than the species Mycoplasma were still unidentified.

The first species of Mycoplasma/Mollicutes, that could be isolated was Mycoplasma mycoides. This bacterium was cultivated by Nocard and Roux in 1898.

In 1956 D.G. Edward and E.A. Freundt made a first proposal for classifying and naming PPLOs. They left undecided, however, whether they belong to the bacteria (prokaryotes, in 1956 called "Schizomycetes") or to the eukaryotes. As type species (name giving species) of the PPLOs/Mycoplasmas Edward and Freundt proposed Mycoplasma mycoides, being the causative organism of "bovine pleuropneumonia" and referring to the "pleuropneumonia-like organisms". Until then Mycoplasma mycoides was known as Asterococcus mycoides, but later that name was recognized as not valid. In their publication of 1956 they described 15 species of Mycoplasma.

In 1967 the class Mollicutes, containing the order Mycoplasmatales, was proposed by the Subcommittee on Taxonomy of the Mycoplasmata.

Now, the name Mycoplasma should exclusively be used for members of the genus Mycoplasma, rather than the use as a trivial name for any mollicute. As the trivial name has been used in literature for a long time, this is yet not always the case.