1. If you were not concerned about detecting H2S production, which ingredients could you leave out of sim media? How would a media missing this ingredient have affected your identification of the organisms used in this lab?
Phenol red broth
1. How would you explain a pink or red tube with a large gas bubble within the Durham tube?
2. How would you interpret a yellow color throughout your control tubes?
3. If phenol red were accidentally left out of the media, what would be the result? Could you recognize that it was left out prior to inoculating your tubes?
1. How would you interpret a blue color throughout your control tube?
2. Could a complex (undefined) media be used for a citrate test?
3. How would you interpret a tube that had growth but that was still green (hint: what would happen if you continued to incubate the tube)?
1. Why is necessary to ensure that bacteria have grown adequately on the media before applying iodine to the plate?
2. Occasionally, when iodine is added to a starch agar plate, the bacteria growth washes loose from the media, becoming completely detached from the surface of the plate. If this were to happen, how would it affect your results?
1. How would the test be affected if the buffer was left out of the media?
2. Urea broth is meant to be read after 24 h incubation. What could happen if the media was allowed to incubate for a longer period of time, such as 96 h?
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1. SIM test media is a complex three-part test that tests at the same time the presence of hydrogen sulfide, indole, or the mobility of the micro-organism. If we do not want to use the sulfide portion of the test, than we can omitted from the media - sodium thiosulfate (as part of the substrate) and ferric ammonium citrate (as an indicator). The above-mentioned ingredients are necessary to identify the occurrence of hydrogen sulfide.
Their absence can make it difficult for us identifying Salmonella spp and its differentiation from Escherichia spp, which requires us great caution in the indole part of the test, which will then be crucial....