MICROBIOLOGY

• Aerobic, fastidious organism.
• The organism lacks a cell wall. Member of the Mollicutes class, among the smallest known free-living bacteria.
  • The lack of cell walls means that beta-lactam antibiotics have no effect.
• Historically, it was known as the "Eaton agent" before its successful cultivation in 1962.
• Believed to be a frequent cause of atypical pneumonia, but historically a problematic diagnosis and serology is often inaccurate.
  • It is not a part of normal human oropharyngeal flora.
  • The organism produces a community-acquired respiratory distress syndrome (CARDS) toxin implicated in colonizing upper airways and pathogenesis as an intracellular pathogen → assists with the invasion of cells.
  • M. pneumoniae culture is difficult.
    • Growth often requires 7-21 days and is successful in 40-90% of cases.
    • Culture media requires heart infusion, peptone, yeast extract, salts, glucose, or arginine, plus fetal calf serum (5-20%).
    • Bacterial overgrowth is a common problem.
• Macrolide resistance is growing worldwide and widespread in China (90% of isolates) and the Western Pacific (53%)[5].
  • Outbreak investigations in the U.S. have found macrolide resistance rates of 8-27%, but the average remains < 10%[5].