Arabinose reaction is used to differentiate Serratia liquefaciens from Serratia marcescens.

• A. Lactose fermentation
• B. Arabinose reaction
• C. Catalase activity
• D. Oxidase reaction

Answer: (B)

Differentiating these Serratia species relies on a specific sugar utilization difference. The arabinose reaction flags whether arabinose is fermented, which is the distinguishing trait between S. liquefaciens and S. marcescens.

S. liquefaciens can ferment arabinose, giving a positive arabinose test result with acid production and a color change in the indicator system. S. marcescens does not ferment arabinose, so its arabinose reaction remains negative. This clear metabolic difference makes the arabinose test the most reliable way to tell the two apart.

Catalase activity and oxidase reaction are general characteristics: most Serratia are catalase positive and oxidase negative, so those tests don’t separate these two species. Lactose fermentation is not consistently definitive for distinguishing them in routine work, so it’s not as useful for this specific differentiation.