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SIM TEST

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SIM (SULFIDE, INDOLE, MOTILITY) MEDIUM


 SIM Medium is designed to allow the detection of sulfide production, indole formation and motility.
Image result for e.coli
Principle
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  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.

FORMULA
Pancreatic Digest of Casein        20.0gm
Peptic Digest of Animal Tissue     6.1gm
Ferrous Ammonium Sulfate         0.2gm
Sodium Thiosulfate  0.2gm
Agar   3.4gm

Final pH 7.3 +/- 0.2 at 25ºC.

Procedure

1. Using isolated colonies from an 18-24 hour culture on solid media, inoculate the SIM Medium by stabbing the center of the medium to a depth of 1/2 inch.
2. Incubate the inoculated medium aerobically at 35ºC. for 18-24 hours.
3. Observe for H2 S production and motility.
4. Once H2 S and motility reaction have been read and recorded, apply three drops of Kovacs Reagent Z67) to the surface of the medium.
5. Observe for the development of a pink to red color.
 RESULTS
 H 2 S test 
1-Negative is denoted by the absence of blackening.
2-Positive is denoted by a blackening of the medium along the line of inoculation. 

1-SULFIDE Negative & 2- SULFIDE Positive
motility test 
negative motility test is indicated by growth confined to the stab line.
positive is indicated by a diffuse zone of growth flaring from the line of inoculation.

Image result for sim test
1-motility negative & 2-motility positive
Indole test:
The top of the medium after addition of Kovacs Reagent
Positive test for indole is show when a pink to red color band is formed at .
Negative not change color

Image result for sim test principle


REFERENCES

www.time2026end.com
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