A community of pneumonia cases occur in college students with atypical features: gradual onset, dry cough, minimal systemic toxicity, patchy interstitial infiltrates, cold agglutinins positive and failure to respond to beta-lactam antibiotics. Culture of Mycoplasma pneumoniae requires special media. Which component is absent from its cell structure that (a) explains antibiotic resistance to beta-lactams and (b) explains its inability to grow on standard media?

• A Absence of a cell wall (peptidoglycan) — explaining beta-lactam resistance; and cholesterol-dependent membrane requiring supplementation in media (SP4 or Hayflick medium with horse serum) ✓
• B Absence of 70S ribosomes causing resistance to aminoglycosides and inability to synthesise enzymes
• C Absence of a nucleus — it is an obligate intracellular organism like Chlamydia
• D Absence of flagella preventing motility and reducing virulence without affecting antibiotic resistance

Explanation

Mycoplasma pneumoniae is unique among bacteria in having no cell wall (peptidoglycan). Consequently, all beta-lactams (which target PBPs in cell wall synthesis) and glycopeptides (vancomycin) are inherently ineffective. Its cell membrane contains cholesterol (unique among prokaryotes), which it must incorporate from the growth medium; standard bacteriological media lack cholesterol, so Mycoplasma requires specialised media (SP4 medium with glucose and serum, or Hayflick medium with horse serum, yeast extract). Treatment is with macrolides (azithromycin) or doxycycline or fluoroquinolones. Cold agglutinins (anti-I IgM) occur in ~50% of Mycoplasma pneumonia.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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