Question

Positive and Negative Control Questions:

Please complete the following table to describe which bacterial species should be used as positive and negative controls for each test. The table at the bottom of this page will help you complete this task. Thenexplains about

What can you learn about a microbe by doing the Phenol Red test, how do you conduct the Phenol Red test?

What does a positive Phenol Red test look like? (mention acid formation and gas formation)

What does a negative Phenol Red test look like?(mention acid formation and gas formation)

	Positive Control Species	Negative Control Species
Catalase
PR-Glucose
PR- Lactose
PR- Sucrose
Oxidase Test

The table below describes the cultures we will have available to use as positive and negative controls.

TEST RESULTS OF AVAILABLE CULTURES:	Catalase	PR- Glucose	PR- Lactose	PR- Sucrose	Oxidase
Alcaligenes (Note* Alcaligenes does not use carbohydrates in its metabolism)	+	-	-	-	+
E. coli	+	+	+	Variable	-
Lactococcus	-	Data Not Available	Data Not Available	Data Not Available	Data Not Available
Pseudomonas	+	-	-	-	+

Answer 1

                                      positive control                    negative control

catalase                                  E.coli                            lactococcus

PR-Glucose                             E.coli                           Pseudomonas

PR-lactose                               E.coli                           Pseudomonas

PR-Sucrose                            E.coli                             Pseudomonas

Oxidase test                             Psedumonas                 E.coli

Phenol red test is used to check carbohydrate metabolism. This test can confirm whether an micro-organism is capable of ferment carbohydrate and as a result acid and gas will be produced.

Phenol red test is caried out in a test tube and inside the test tube a small tube is placed which is called as Durhum tube. This Durhum tube is required for the gas production. In priniciple the colour of the broth will change of the broth as a result of the fermentation. When fermentation occurs, acid is produced which will change the colour of the phenol red.

If the test sample is able to ferment carbohydrate, then the colour of the phenol red turns to yellow and gas is produced in Durhum tube. The gas is visualized in the form of bubble.

If the test sample is not able to ferment carbohydrate, then phenol red solution will turn red or purple and there will be no gas formation, so no bubbles will be there at Durhum tube.