Which statement best describes the Gram stain appearance of Legionella in respiratory specimens?

• A. Numerous neutrophils with few organisms seen
• B. Abundant Gram-positive cocci in chains
• C. Gram-negative diplococci inside neutrophils
• D. Filamentous Gram-positive rods

Answer: (A)

Legionella in respiratory specimens is a fastidious organism that is usually present in only small numbers, even though the inflammatory response drives many neutrophils into the area. On a routine Gram stain, you typically see lots of neutrophils with only a few organisms visible, reflecting the low bacterial load and the staining challenges with Legionella. The organisms themselves are Gram-negative bacilli, but they are often scant and can be overlooked on Gram stain, which is why the pattern described as many neutrophils with few organisms seen best fits Legionella.

The other descriptions point to different pathogens or appearances: Gram-positive cocci in chains would suggest streptococci; Gram-negative diplococci inside neutrophils would suggest Neisseria species; filamentous Gram-positive rods would indicate Actinomyces.