Violet-colored colonies are typically produced by which organism?

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

Answer: (A)

Pigment production by bacteria provides a quick visual clue for identification. Chromobacterium violaceum is famous for making violacein, a pigment that gives its colonies a violet to purple color on many culture media. This distinctive violet coloration helps distinguish it from other organisms that produce different pigments. For example, Pseudomonas aeruginosa typically forms blue-green colonies due to pyocyanin, Serratia marcescens often appears red from prodigiosin especially at room temperature, and Chryseobacterium meningosepticum can produce yellow pigmented colonies. So, the violet color is most characteristic of Chromobacterium violaceum, though pigment alone isn’t definitive and should be followed up with confirmatory tests.