Sellers Differential HiVeg™ Agar

Principle and Interpretation

Sellers Differential HiVeg Agar is prepared by using HiVeg peptone in place of Peptic digest of animal tissue making the medium free of BSE/TSE risks. Sellers Differential HiVeg Agar is the modification of Sellers Differential Agar which is formulated as described by Sellers (1) for differentiation and identification of non-fermentative gram-negative bacilli especially Pseudomonas aeruginosa, Acinetobacter calcoaceticus and also Alcaligenes faecalis. The medium is complex with differentiation based on oxidation of dextrose, fluorescence, production of nitrogen and pH changes.

Yeast extract and HiVeg peptone are the sources of carbon and nitrogen compounds as well as vitamins and minerals. Pseudomonas aeruginosa usually oxidizes glucose, producing an acid reaction; however in this medium it does not, due to the presence of arginine and high peptone concentration. The alkali produced from peptone breakdown neutralizes acid (3). Oxidation of dextrose by the organisms is readily visible as a yellow band at the slant-butt junction. D-Mannitol and magnesium sulphate stimulate fluorescence while nitrogen gas production is stimulated by dipotassium phosphate (1, 2). Sodium nitrate and nitrite serve as substrates for the production of nitrogen gas for denitrifying bacteria. Phenol red and bromo thymol blue are the pH indicators. Arginine dihydrolase positive reaction is indicated by the formation of blue colour.