• Distinguished from other prokaryotes and placed in the class Mollicutes because they lack a true cell wall and consequent rigidity.
  • This is a stable characteristic exhibited by the genera Mycoplasma, Ureaplasma and Acholeplasma and is distinct from cell wall-deficient and L-forms of other species.
  • The outer membrane, the outermost layer, functions as the major antigenic interface.
  • It is a flexible triple-layered structure of proteins and liquids.
  • Many species also contain cholesterol in the membrane, which is absent from other bacterial cells.
  • The important species is M. pneumoniae, but M. hominis and U. urealyticum may cause genital tract infection.


  • Transmission of M. pneumoniae from person to person by airborne route.
  • Other mycoplasmas and ureaplasmas can be transmitted by sexual contact.


  • M. pneumoniae is an important cause of ‘atypical pneumonia’.
  • Mycoplasma also associated with genital infection and with joint and other inflammatory infections.
  • Other mycoplasmas are important pathogens of animals and birds.

Laboratory Identification:

  • Many subspecies are fastidious, and complex media and soft agar may be required for satisfactory culture.
  • Cultures incubated for at least seven days although some species grow readily on moist blood agar plates within 48 hours.
  • Cells very variable in size (up to 100 µm) and morphology; cannot be stained by Gram’s stain, but impression of colonies can be stained with Romanowsky’s stains.
  • Diagnosis of infection based on serology due to difficulties of culture.