"Mycoplasmas" is the trivial name for a complex and unique group of bacteria occurring in humans, animals, plants and insects.
Biological Features & Taxonomy
Mycoplasmas belong to the bacterial class Mollicutes (meaning “soft skin”), and are characterized by
- a small cell size (0,3 – 0,8 µm average)
- the lack of a cell wall
- a small genome size (0.58 - 2.2 Mbp) and
- a low G+C content (23 - 40 mol %) in their genomes
More than 200 mycoplasma species have been described. They have been classified into the following 9 genera:
Acholeplasma, Anaeroplasma, Asteroleplasma, Entomoplasma, Mesoplasma, Mycoplasma, Spiroplasma, Ureaplasma, Candidatus Phytoplasma
Among these, the genus Mycoplasma is the largest group comprising more than 100 described species which also includes the new group of haemotrophic mycoplasmas or “haemoplasmas” representing red blood cell parasites formerly belonging to the rickettsiae. A number of Mycoplasma and Ureaplasma species are human and animal pathogens.
Mycoplasmas as Infectious Agents
The role of mycoplasmas as agents of infection and disease has for a long time been largely ignored because of two reasons: (1) the widespread, but misguided clinical perception that these bacteria are unimportant, and (2) the lack of rapid diagnostic procedures for mycoplasma detection. This situation has changed because of the greater acceptance of the clinical importance of these organisms as pathogens and the improvement of detection methods.
Among the more than 18 human mycoplasma species, the following five are agents of infection and disease: Mycoplasma pneumoniae, Mycoplasma hominis, Mycoplasma genitalium, Ureaplasma urealyticum and Ureaplasma parvum.
Of these human pathogens, M. pneumoniae is a leading cause of respiratory tract infections in particular in children and young adults the most important one; up to 10% of patients develop pneumonia.
Mycoplasmas are also often found in the respiratory tract of cattle, sheep, goats, swine, horses, small laboratory animals, poultry etc. Most of these mycoplasma species are commensals, and only a small number of species are agents of clearly identifiable respiratory diseases, such as Mycoplasma bovis in cattle, Mycoplasma hyopneumoniae in swine, and Mycoplasma gallisepticum in poultry, leading to enormous economic losses in the milk and meat industry.
Besides respiratory diseases, the main clinical manifestations of mycoplasma diseases in animals are mastitis, arthritis, serositis and genital disorders/infertility.