Which organism is known for producing a violet pigment?

• A. Chryseobacterium meningosepticum
• B. Chromobacterium violaceum
• C. Pseudomonas aeruginosa
• D. Serratia marcescens

Answer: (B)

Pigment production by bacteria is a handy diagnostic clue because different species synthesize distinct colored compounds that color the colonies. The violet pigment violacein is characteristic of Chromobacterium violaceum, so its colonies appear deep purple on standard media. This organism is a Gram-negative, nonfermenting rod commonly found in soil and water, and its violet pigment is a classic identifying feature. Other choices produce different colors: Chryseobacterium meningosepticum often forms yellow pigmented colonies; Pseudomonas aeruginosa yields blue-green pyocyanin (and yellow-green pyoverdin) pigments; Serratia marcescens can produce a red pigment called prodigiosin, especially at room temperature. Because the violet pigment uniquely points to Chromobacterium violaceum, it is the best answer.