A colour test used to differentiate among the family Enterobacteriaceae, which consists of
adding alpha-naphthol, then KOH to Voges-Proskauer broth, which has been inoculated with bacteria
• V-P positive (bright red colour) Enterobacter, Klebsiella, Serratia, Hafnia alvei, Vibrio eltor, Vibrio alginolyticus
• V-P negative (yellow brown) Citrobacter sp., Shigella, Yersinia, Edwardsiella, Salmonella, Vibrio furnissii, V fluvialis, V vulnificus, and V parahaemolyticus.
• V-P variable Erwinia