Microbiology Encyclopedia

Mycoplasma pneumoniae

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tagsorganism, bacteriology, atypical, respiratory

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Mycoplasma pneumoniae

One-Sentence Definition

Mycoplasma pneumoniae is a wall-less bacterium (Mollicutes) that causes atypical (“walking”) pneumonia and extrapulmonary disease, undetectable by Gram stain and intrinsically resistant to β-lactams.

Taxonomy & Morphology

  • No peptidoglycan Bacterial Cell Wall — trilaminar membrane with sterols
  • Among smallest free-living bacteria; fried-egg colonies on special media (slow)
  • Related genera: Ureaplasma, Mycoplasma genitalium (STI / AMR importance)

Virulence Highlights

  • P1 adhesin — attachment to respiratory epithelium
  • Community-acquired respiratory distress syndrome (CARDS) toxin
  • Molecular mimicry → autoimmune extrapulmonary phenomena (e.g., cold agglutinins)

Clinical Syndromes

  • Tracheobronchitis; community atypical pneumonia (school-age, young adults)
  • Extrapulmonary: rash, encephalitis, hemolysis (cold agglutinins), mucositis
  • Outbreaks in closed populations (schools, barracks)

Diagnosis

  • PCR preferred (sensitivity/specificity)
  • IgM/IgG serology — timing limits acute use
  • Culture rarely used clinically (slow, specialized)
  • Chest imaging often patchy; Gram stain of sputum unhelpful for organism visualization

Treatment Notes (conceptual)

  • Macrolides first-line historically; doxycycline / fluoroquinolones alternatives
  • β-lactams never appropriate (no cell wall target)
  • Rising macrolide resistance in Asia and elsewhere — know local rates

AMR

  • Macrolide resistance via 23S rRNA mutations — detectable by PCR/WGS
  • M. genitalium is a more extreme AMR problem (azithromycin/moxifloxacin failure)

Genomics & Computational Notes

Active Recall

  1. Why do penicillins fail against Mycoplasma?
  2. Preferred acute diagnostic method?
  3. Mechanism class of macrolide resistance?

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