Motility-Indole-Lysine HiVeg™ Medium (MIL HiVeg™ Medium)

Principle and Interpretation

This medium is prepared by completely replacing animal based peptone with vegetable peptones making the medium free of BSE/TSE risks. MIL HiVeg Medium is the modification of MIL Medium which is formulated according to Reller and Merrett (1). It provides 4 differential reactions in a single culture tube. It is recommended to use along with Triple Sugar Iron (TSI) HiVeg Agar (MV021) and Urea HiVeg Agar Base (MV112) so as to enable initial identification of members of Enterobacteriaceae. HiVeg peptone, HiVeg hydrolysate provides amino acids and other complex nitrogenous substances. Yeast extract is added to supply the B-complex vitamins. Dextrose is a source of energy. Bromocresol purple is a pH indicator which facilitate detection of decarboxylase activity. Due to dextrose fermentation the colour of the medium changes from purple to yellow. The acidic pH also stimulates enzyme activity. The production of amines due to degradation of amino acid elevates the pH and turns the medium at the bottom of the tube to purple. Due to the higher oxygen tension, the upper portion of the tube remains acidic (yellow). Oxidative deamination of lysine yields a compound which reacts with ferric ammonium citrate, giving reddish colour at the top of the medium (2). Cultures are stab-inoculated and incubated at 37°C for 18-24 hours. Motility, lysine deamination and lysine decarboxylation reactions are read before testing indole reaction. Motility is indicated by diffused growth. Non-motile cultures grow along with stab line. Lysine deamination is observed as red or red-brown colour at the top of the medium while decarboxylation shows a purple colour throughout the medium. This colour may vary in intensity, may be a light colour due to reduction of indicator. For testing indole production add 3-4 drops of Kovac's reagent (R008) to the medium. A pink to red coloured ring indicates a positive reaction.