A relatively slow growing and fastidious, gram-negative rod that produces a characteristic brown pigment on Feeley-Gorman Agar is

The organism described is Legionella pneumophila, which is a slow-growing and fastidious gram-negative rod. One of its distinguishing features is its ability to produce a characteristic brown pigment when cultured on Feeley-Gorman Agar, a selective medium that supports the growth of Legionella species while inhibiting others. This pigment production is a key aspect to look for in the identification of this bacterium.

Legionella pneumophila is particularly notable for its association with pneumonia, known as Legionnaires' disease, and is often found in water environments. Its fastidious nature requires special culturing conditions that are not typical for most other bacteria, further emphasizing why it is crucial to recognize its growth characteristics when making an identification.

The other organisms listed have different culture requirements and do not produce the same characteristic brown pigmentation on agar. For instance, Haemophilus influenzae requires specific growth factors and does not produce a brown pigment in this context, while Bordetella pertussis also has unique growth requirements and does not grow on Feeley-Gorman Agar. Brucella melitensis is a gram-negative coccobacilli typically associated with brucellosis and has its own specific culture requirements. This further highlights the uniqueness of Legionella pneumoph