for determination of hydrogen sulphide production, indole formation and motility of enteric bacilli. SIM Medium is used to differentiate enteric bacilli particularly Salmonella and Shigella on the basis of sulphide production, indole formation and motility. Jordan and Victorson reported that Salmonella paratyphi A and paratyphi B can be distinguished on the basis of H2S production using lead acetate. Sulkin and Willett used Triple Sugar Iron Agar with 1% agar for motility along with H2S production and carbohydrate fermentation. Sosa described a peptone medium with low agar for motility and indole determination. Greene et al. used SIM Medium to detect motility in a large series of cultures of typhoid organisms
Peptonized iron and sodium thiosulphate are the indicators of H2S production. This H2S reacts with peptonized iron to form black precipitate of ferrous sulphide.Peptone and Beef extract provides nitrogeneous and carbonaceous compounds, long chain amino acids, vitamins and other essential nutrients. Tryptophan from peptone, is degraded by specific bacteria to produce indole. The indole is detected by the addition of chemical reagents following the incubation period. SIM Medium is a semi-solid, due to the low concentration of agar. The semi-solid nature of this medium allows for easy visual determination of motility which appears as growth extending outward from the original line of inoculation.