Which genus is most likely the yellow, nonfermentative gram-negative bacillus isolated from nebulizers?

• A. Chryseobacterium
• B. Pseudomonas
• C. Alcaligenes
• D. Moraxella

Answer: (A)

A yellow pigment together with a nonfermentative Gram-negative rod that is often found in hospital water and on devices like nebulizers points to Chryseobacterium. These bacteria belong to the Flavobacteriaceae family and produce yellow carotenoid pigments that color their colonies, which helps distinguish them from other nonfermenters. They are environmental organisms frequently implicated in contamination of hospital water systems and respiratory equipment, so nebulizers are a recognized source. In contrast, Pseudomonas typically shows different pigment patterns (often blue-green from pyocyanin) and Moraxella are diplococci rather than bacilli, while Alcaligenes lacks the distinctive yellow pigment. Thus the yellow pigment–producing, nonfermentative Gram-negative rod aligns best with Chryseobacterium.