Phenol Red Broth PDF

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Lab Assignment about the Phenol Red Brot...

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Ali Gilblair Phenol Red Broth

Phenol red broth is a general-purpose differential test medium usually used to differentiate gram negative enteric bacteria. This experiment tests for the presence of acid and/or gas produced from carbohydrate fermentation. This broth contains peptone, phenol red (pH indicator) a Durham tube, and a carbohydrate. There are three different phenol red broths used, one that contains glucose, one that contains lactose, and the last that contains sucrose. The objective of phenol red is to determine which organism can utilize each of the different sugars. Phenol red is the pH indicator, so it turns yellow below a pH of 6.8 and red/fuchsia about a pH of 7.4. The media turns yellow if the organism is able to utilize the carbohydrate, which produces an acid by-product and produces an air bubble that is trapped in the Durham tube. Sometimes an orange color can be seen which represents a pH higher than 6.8 but should not be considered positive. A positive in acid production result will show the liquid in the tube turning yellow and a negative result will show that the liquid remains red, indicating the bacteria cannot ferment the carbohydrate present in that media. In gas production, a positive result will show a bubble in the inverted Durham tube, and a negative result will show no bubble....