Cronobacter sakazakii is notable among Enterobacteriaceae for producing which pigment on media?

• A. Pink pigment
• B. Yellow pigment
• C. Green pigment
• D. No pigment

Answer: (B)

Pigment production by colonies is a useful clue in identifying certain Enterobacteriaceae. Cronobacter sakazakii is notable because it commonly produces a yellow pigment when grown on standard lab media, so its colonies appear distinctly yellow rather than pale or colorless. This yellow coloration, due to a carotenoid-type pigment, helps distinguish it from many related bacteria whose colonies are nonpigmented under routine conditions (and from others that show different colors). The pigment’s presence can depend on growth conditions like temperature and the medium used, which is why the yellow hue is a helpful, consistent trait to look for. Pink or green pigments are associated with other organisms, and no pigment at all is not characteristic of Cronobacter sakazakii, making yellow the best descriptor of its appearance on media.