Legionella pneumonia is treated with which antibiotic options?

• A. Penicillin G
• B. Macrolides or respiratory fluoroquinolones
• C. Cephalexin
• D. Amoxicillin

Answer: (B)

Legionella pneumonia is caused by an intracellular bacterium that replicates inside alveolar macrophages, so the antibiotics chosen must penetrate cells well and act against intracellular organisms. Beta-lactam antibiotics like penicillins and cephalosporins generally have limited intracellular penetration and are not reliably effective against Legionella. In contrast, macrolides (for example, azithromycin) and respiratory fluoroquinolones (for example, levofloxacin, moxifloxacin) achieve high intracellular concentrations and are active against Legionella by inhibiting protein synthesis or DNA replication, respectively. This intracellular activity makes them the preferred treatment options.