Hippurate hydrolysis. Emulsify generous 2 mm loopful of growth from the restreaked pick on the nonselective or antibiotic
inhibition plate to 0.4 ml 1% hippurate solution in 13 x 100 mm tube. Incubate 2 h in 37°C water bath. Add 0.2 ml ninhydrin
reagent (R47), agitate, and reincubate 10 min. Violet (not medium or pale purple) color is positive reaction. Only C. jejuni is
hippurate-positive. Refrigerate hippurate solution up to 1 month and ninhydrin solution up to 3 months.