What kind of bacteria is Legionella pneumophila?

• A. Gram-negative bacillus
• B. Gram-positive cocci
• C. Gram-positive bacillus
• D. Gram-negative cocci

Answer: (A)

Legionella pneumophila is a Gram-negative bacillus. This means it has a thin peptidoglycan layer and an outer membrane with lipopolysaccharide, which influences how it stains and how it responds to antibiotics. Its rod-shaped form makes it a bacillus rather than a cocci, so it’s not a Gram-positive organism and not spherical. In the lab, detection can be tricky with standard Gram stains and routine culture, often requiring specialized media and staining methods. With all that in mind, the description that best fits Legionella pneumophila is a Gram-negative bacillus.