Mycoplasma

Mycoplasma is a genus of bacteria in the family Mycoplasmataceae, within the class Mollicutes. Members of this genus are among the smallest free-living microorganisms and are characterized by the absence of a rigid cell wall. Their membranes contain cholesterol, giving them pleomorphic shapes. They colonize mucosal surfaces of humans and animals and can be commensal or pathogenic.

They lack peptidoglycan cell walls, which makes them inherently resistant to many antibiotics that target cell wall synthesis, such as beta-lactams. They are extremely small and have fastidious growth requirements, growing slowly on specialized media, such as SP-4 or Eaton's agar with serum and cholesterol. Colonies can be very small, and M. pneumoniae is notable for forming fried-egg colonies on such media.

Human pathogens include M. pneumoniae, which causes atypical pneumonia and tracheobronchitis, especially in young adults; M. genitalium and M. hominis cause nongonococcal urethritis and cervicitis; M. fermentans has been reported in various disputed associations with disease. Other Mycoplasma species affect animals, especially M. gallisepticum and M. synoviae in birds, and M. bovis and related species in cattle and other livestock.

Diagnosis involves culture, serology, and molecular methods such as PCR; culture is slow and non-specific. Treatment relies on agents that do not act on cell walls, including macrolides, tetracyclines, and fluoroquinolones. Because of variability and resistance, susceptibility testing is used in some settings and treatment choices may depend on the specific species.