SIM Medium
SIM stands for Sugar, Indole, and Motility as this medium runs three microbiological tests in one tube at the same time: the Indole test, the Hydrogen Sulfide production test, and the Motility test. SIM medium is a semi-solid medium containing protein, iron, sulfur as sodium thiosulfate, and only a little agar. The semi-solid medium (about 0.4% agar) allows for the testing of the motility of a strain. The agar is at a concentration to allow the bacteria to move through a gel. The protein sources allow for the testing of the production of Indole. Indole is formed (along with pyruvate and amonia) when the enzyme tryptophanase degrades the amino acid tryptophan in protein (this usually occurs when bacteria degrade protein). Hydrogen sulfide is produced if the sodium thiosulfate is reduced by the bacterial strain. This happens when the strain either degrades the amino acid cysteine during protein degradation, or when anaerobic respiration shuttles the electrons to sulfur instead of to oxygen. In either case H2S is produced (hydrogen sulfide) which reacts with the iron compound to form the black precipitate of ferric sulfide. The black color acts as an indicator for the presence of hydrogen sulfide.
Composition
Ingredients
Gms / Litre HM Peptone B# 3.000
Peptone 30.000
Peptonized iron 0.200
Sodium thiosulphate 0.025
Agar 3.000 Final pH ( at 25°C) 7.3±0.2
Formula adjusted, standardized to suit performance parameters
Purpose: see Indole, Motility, and Hydrogen Sulfide production tests.
Procedure:
Obtain your tube containing SIM medium (1 tube/strain being tested).
Label the tube, including your name, the date, and the test name.
Do NOT use your Wire loop, as this will soon ruin it. Use your inoculating needle.
Care must be taken here, as you must perform your stab correctly or the test may fail. Be certain that the needle is straight and that your stab is straight down and then pulled up exactly the way it went down.
Aseptically transfer your bacteria to the inoculating needle. This is done by flaming your needle (not the loop), COOLING IT WELL, picking up bacteria on the needle by rolling the tip in a colony of bacteria. Sometimes students get no growth in this test from just briefly cooling the tip of the needle, the heat from above the tip moves down the needle and kills their bacteria.
Now stab the needle straight down into the tube going about 2/3 of the way down and then pulling the needle straight out the way you came in.
A poor stab will make your reading of the results difficult, so repeat the test if needed.
Remind your instructor to set up a control tube (an uninoculated control). Gently place your tubes in the rack where instructed. Rough handling may distort the test.
Incubate the tubes at room temperature for about 5 days (or at 35-37 C for 1-2 days).
Results:
You will need to follow the results for three separate tests: Motility, Hydrogen Sulfide production, and Indole.
Perform these tests in the above order. The Motility test is performed first because it is the most likely test to be disrupted by excessive handling, Hydrogen Sulfide is done next because it is only making an observation, and the Indole test is done last because it will change the tube.
Type of specimen Pure culture isolate
After use, contaminated materials must be sterilized by autoclaving before discarding. Specimen Collection and Handling:
Warning and Precautions : Read the label before opening the container. Wear protective gloves/protective clothing/eye protection/ face protection. Follow good microbiological lab practices while handling specimens and culture. Standard precautions as per established guidelines should be followed while handling specimens. Safety guidelines may be referred in individual safety data sheets.
SIM stands for Sugar, Indole, and Motility as this medium runs three microbiological tests in one tube at the same time: the Indole test, the Hydrogen Sulfide production test, and the Motility test. SIM medium is a semi-solid medium containing protein, iron, sulfur as sodium thiosulfate, and only a little agar. The semi-solid medium (about 0.4% agar) allows for the testing of the motility of a strain. The agar is at a concentration to allow the bacteria to move through a gel. The protein sources allow for the testing of the production of Indole. Indole is formed (along with pyruvate and amonia) when the enzyme tryptophanase degrades the amino acid tryptophan in protein (this usually occurs when bacteria degrade protein). Hydrogen sulfide is produced if the sodium thiosulfate is reduced by the bacterial strain. This happens when the strain either degrades the amino acid cysteine during protein degradation, or when anaerobic respiration shuttles the electrons to sulfur instead of to oxygen. In either case H2S is produced (hydrogen sulfide) which reacts with the iron compound to form the black precipitate of ferric sulfide. The black color acts as an indicator for the presence of hydrogen sulfide.
Composition
Ingredients
Gms / Litre HM Peptone B# 3.000
Peptone 30.000
Peptonized iron 0.200
Sodium thiosulphate 0.025
Agar 3.000 Final pH ( at 25°C) 7.3±0.2
Formula adjusted, standardized to suit performance parameters
Purpose: see Indole, Motility, and Hydrogen Sulfide production tests.
Procedure:
Obtain your tube containing SIM medium (1 tube/strain being tested).
Label the tube, including your name, the date, and the test name.
Do NOT use your Wire loop, as this will soon ruin it. Use your inoculating needle.
Care must be taken here, as you must perform your stab correctly or the test may fail. Be certain that the needle is straight and that your stab is straight down and then pulled up exactly the way it went down.
Aseptically transfer your bacteria to the inoculating needle. This is done by flaming your needle (not the loop), COOLING IT WELL, picking up bacteria on the needle by rolling the tip in a colony of bacteria. Sometimes students get no growth in this test from just briefly cooling the tip of the needle, the heat from above the tip moves down the needle and kills their bacteria.
Now stab the needle straight down into the tube going about 2/3 of the way down and then pulling the needle straight out the way you came in.
A poor stab will make your reading of the results difficult, so repeat the test if needed.
Remind your instructor to set up a control tube (an uninoculated control). Gently place your tubes in the rack where instructed. Rough handling may distort the test.
Incubate the tubes at room temperature for about 5 days (or at 35-37 C for 1-2 days).
Results:
You will need to follow the results for three separate tests: Motility, Hydrogen Sulfide production, and Indole.
Perform these tests in the above order. The Motility test is performed first because it is the most likely test to be disrupted by excessive handling, Hydrogen Sulfide is done next because it is only making an observation, and the Indole test is done last because it will change the tube.
Type of specimen Pure culture isolate
After use, contaminated materials must be sterilized by autoclaving before discarding. Specimen Collection and Handling:
Warning and Precautions : Read the label before opening the container. Wear protective gloves/protective clothing/eye protection/ face protection. Follow good microbiological lab practices while handling specimens and culture. Standard precautions as per established guidelines should be followed while handling specimens. Safety guidelines may be referred in individual safety data sheets.
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