SIM HiVeg™ Medium

Principle and Interpretation

SIM HiVeg Medium is prepared by replacing animal peptones like Peptic digest of animal tissue, Beef extract and Peptonized iron with vegetable peptones like HiVeg peptone, HiVeg extract and HiVeg peptonized iron respectively. This makes the medium free from BSE/TSE risks. SIM HiVeg Medium is the modification of animal based SIM medium. SIM HiVeg Medium is used to differentiate enteric bacilli (Salmonella and Shigella) on the same principles as in SIM medium i.e.on basis of sulphide production, indole formation and motility (1, 2). It is known that Salmonella serotype Paratyphi A and Salmonella serotype Paratyphi B can be distinguished on the basis of H₂S (hydrogen sulphide) production using lead acetate as reported by Jordan and Victorso (3). Medium with low agar helps to determine motility and indole production (4) HiVeg peptonized iron and sodium thiosulphate are the indicators of H₂S production. H₂S reacts with HiVeg peptonized iron to form black precipitate of ferrous sulphide. Motile organisms intensify the H₂S reaction. Motile organisms grow away from line of inoculation showing diffused growth while non-motile organisms grow along the stab line. Tryptophan present in HiVeg peptone is degraded by specific bacteria to produce indole (2). Indole is detected by the addition of chemical reagents following incubation period. Add 0.2 ml of Kovac's reagent to the tube and allow to stand for 10 minutes. A pink to red coloured ring indicates a positive indole reaction.