A 35-year-old with atypical pneumonia shows 'walking pneumonia' pattern — lobar opacity on X-ray but ambulant patient. Cold agglutinin titre is 1:512. Sputum Gram stain is unremarkable. The causative organism lacks a cell wall, making it resistant to:
- A Beta-lactams (penicillin, cephalosporins) ✓
- B Macrolides (azithromycin)
- C Tetracyclines (doxycycline)
- D Fluoroquinolones (levofloxacin)
Correct answer: A. Beta-lactams (penicillin, cephalosporins)
Explanation
Mycoplasma pneumoniae lacks a cell wall and therefore is intrinsically resistant to all beta-lactam antibiotics (penicillins, cephalosporins, carbapenems) that target peptidoglycan synthesis. It is treated with macrolides (azithromycin — first-line), tetracyclines (doxycycline), or fluoroquinolones (levofloxacin). Cold agglutinins (anti-I IgM) at high titres are characteristic of M. pneumoniae infection.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.