Sim method

 PRINCIPLE:

The formulation of SIM Medium is designed to allow the detection of sulfide production, indole formation and motility.The medium contains ferrous ammonium sulfate and sodium thiosulfate, which together serve as indicators for the production of hydrogen sulfide. Hydrogen sulfide production is detected when ferrous sulfide, a black precipitate, is produced as a result of ferrous ammonium sulfate reacting with H2 S gas. Casein peptone, another component of SIM Medium, is rich in tryptophan. Organisms possessing the enzyme tryptophanase degrade tryptophan to indole. Indole is detected upon the addition of Kovacs Reagent (Cat. no. Z67) following incubation of the inoculated medium. Indole combines with p-dimethylaminobenzaldehyde and produces a red band at the top of the medium. A negative indole test produces no color change upon the addition of Kovacs Reagent. The small amount of agar added to the medium provides a semi-solid structure allowing for the detection of bacterial motility. Motile organisms extend from the stab line and produce turbidity or cloudiness throughout the medium. Non-motile organisms grow only along the stab line and leave the surrounding medium clear. SIM Medium also contains animal tissue which provides amino acids and nutrients necessary for bacterial growth.

A positive H 2 S test is denoted by a blackening of the medium along the line of inoculation. A negative H 2 S test is denoted by the absence of blackening.

A positive motility test is indicated by a diffuse zone of growth flaring from the line of inoculation.

A negative motility test is indicated by growth confined to the stab line.

A positive test for indole is denoted when a pink to red colour band is formed at the top of the medium after addition of Kovacs Reagent. A yellow colour denotes a negative indole.