Which type of pneumonia presents in a lobar pattern and is classically treated with Penicillin G?

• A. Haemophilus influenzae
• B. Legionella
• C. Pneumococcal
• D. Mycoplasma

Answer: (C)

Lobar consolidation on imaging points to pneumococcal pneumonia, caused by Streptococcus pneumoniae. This organism fills an entire lobe with inflammatory exudate, producing a dense, homogeneous opacity often with air bronchograms. Penicillin G has classically been the treatment of choice because susceptible pneumococcal strains are inhibited by penicillin's inhibition of bacterial cell wall synthesis. In contrast, Haemophilus influenzae more often causes bronchopneumonia with patchy, multilobar involvement and may require beta-lactamase–stable or broader-spectrum agents; Legionella and Mycoplasma typically present with atypical or interstitial patterns and are treated with macrolides or doxycycline rather than penicillins.