A 22-year-old college student presents with gradual onset fever, dry cough, and bilateral lower lobe infiltrates on chest X-ray disproportionate to his mild clinical condition. Cold agglutinin titer is elevated. The causative organism lacks a cell wall and cannot be Gram-stained. The drug of choice is:

• A Amoxicillin
• B Cefuroxime
• C Vancomycin
• D Azithromycin ✓

Explanation

Mycoplasma pneumoniae causes atypical (walking) pneumonia and is the most common cause of community-acquired pneumonia in young adults. Because it completely lacks a cell wall, it cannot be Gram-stained and is intrinsically resistant to all beta-lactams (penicillins, cephalosporins) and glycopeptides (vancomycin) which target cell wall synthesis. Macrolides (azithromycin, clarithromycin) and doxycycline are the drugs of choice. Cold agglutinins (IgM anti-I antibodies) are produced in about 50% of cases, though Mycoplasma IgM serology or PCR is more specific.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.