Which organism produces a positive phenylalanine deaminase reaction?

Which organism produces a positive phenylalanine deaminase reaction?

• A. Citrobacter freundii
• B. Klebsiella pneumoniae
• C. Providencia stuartii
• D. Yersinia enterocolitica

Answer: (C)

Phenylalanine deaminase activity identifies bacteria that can remove the amino group from phenylalanine to form phenylpyruvic acid, which, when ferric chloride is added, gives a green color if present. Among common Enterobacteriaceae, PAD activity is found in the Proteae group, including Providencia species. Providencia stuartii readily produces phenylalanine deaminase, so the test yields a positive (green) result. The other listed organisms typically lack this enzyme, so they do not develop the green color and show a negative reaction.

Phenylalanine deaminase activity identifies bacteria that can remove the amino group from phenylalanine to form phenylpyruvic acid, which, when ferric chloride is added, gives a green color if present. Among common Enterobacteriaceae, PAD activity is found in the Proteae group, including Providencia species. Providencia stuartii readily produces phenylalanine deaminase, so the test yields a positive (green) result. The other listed organisms typically lack this enzyme, so they do not develop the green color and show a negative reaction.