Crystal Violet Tetrazolium HiVeg™ Agar Base

Principle and Interpretation

Crystal Violet Tetrazolium HiVeg Agar Base is prepared by using HiVeg hydrolysate instead of Casein enzymic hydrolysate making the medium free of BSE/TSE risks. This medium is the modification of Crystal Violet Tetrazolium Agar Base which is based on the original formulation suggested by Olson (1) and recommended by APHA (2) for detecting gram-negative psychrotrophic bacteria causing food spoilage. Species of Achromobacter, Alcaligenes, Flavobacterium and Pseudomonas are included among the psychrotrophic bacteria as they have their growth optima below 20°C (3). Many psychrotrophic microorganisms when present in high density can cause off-flavours and physical spoilage of foods. Their growth rate is highly dependent on temperature, if the temperature is reduced their growth rate is slowed down. Thus the spoilage of refrigerated food is very much dependent on temperature (3, 4).

HiVeg hydrolysate and yeast extract provide various nitrogenous nutrients to the organisms while dextrose serves as the carbon or carbohydrate source. Crystal violet inhibits most of the gram-positive organisms and therefore inclusion of crystal violet in the medium does not affect the growth of psychrotrophic organisms which are mostly gram-negative.