Mycoplasma pneumoniae causes atypical pneumonia. A key diagnostic feature that differentiates it from typical bacterial pneumonia is:
- A Positive Gram stain of sputum showing gram-positive diplococci
- B Failure to grow on standard culture media due to absence of cell wall; detected by cold agglutinins, serology, or NAAT ✓
- C Chest X-ray showing lobar consolidation with air bronchograms
- D Marked neutrophilia >15,000/µL on blood count
Correct answer: B. Failure to grow on standard culture media due to absence of cell wall; detected by cold agglutinins, serology, or NAAT
Explanation
Mycoplasma pneumoniae lacks a cell wall, cannot be Gram stained, and does not grow on routine blood or chocolate agar. Detection relies on serology (complement fixation or IgM/IgG ELISA — ≥4-fold titre rise or single high IgM), cold agglutinins (IgM against I antigen on RBCs, present in ~50%), or PCR from throat swab/sputum. Chest X-ray typically shows bilateral interstitial/patchy infiltrates (atypical pattern), not lobar consolidation. Blood count shows lymphocytic predominance rather than neutrophilia.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.