MICROBIOLOGY

• Aerobic, fastidious organism.
• Organism lacks a cell wall. Member of Mollicutes class, among the smallest known free-living bacteria.
  • Lack of cell wall means that beta-lactam antibiotics have no effect.
• Historically termed the "Eaton agent," prior to successful cultivation in 1962.
• Believed to be a frequent cause of atypical pneumonia but historically a difficult diagnosis and serology inaccurate often.
  • Not a part of normal human oropharyngeal flora.
  • The organism produces community-acquired respiratory distress syndrome (CARDS) toxin implicated in the colonization of upper airways and pathogenesis as intracellular pathogen → assists with the invasion of cells.
  • M. pneumoniae culture is difficult. Growth often requires 7-21 days, successful in 40-90% of cases.
    • Culture media requires heart infusion, peptone, yeast extract, salts, glucose or arginine + fetal calf serum (5-20%).
    • Bacterial overgrowth a common problem.
• Macrolide resistance growing issue worldwide and especially common in China (90% of isolates).
  • Outbreak investigations in the U.S. have found macrolide resistance rates of 8-27%.