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Principle
- SIM Medium is used for the differentiation of enteric bacteria on the basis of three different characteristics, H2S Production, motility, and Indole production. The media is composed of special peptone, peptone, peptonized iron, sodium thiosulphate, and agar.
- Peptone and special peptone provides nitrogenous and carbonaceous compounds, long-chain amino acids, vitamins, and other essential nutrients. Special peptone contains tryptophan, which is degraded by specific bacteria to produce Indole.
- The Indole is detected by the addition of chemical reagents following the incubation period. Peptonized iron and sodium thiosulphate are the indicators of H2S production.
- This H2S reacts with peptonized iron to form a black precipitate of ferrous sulphide. Motile organisms exaggerate the H2S reaction. Motile organisms grow away from the line of inoculation showing diffused growth while non-motile organisms grow along the stab line.
- Motility detection is possible due to the semisolid nature of the medium. Growth radiating out from the central stab line indicates that the test organism is motile.
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