Review Questions 1. Although Methyl Red Test and...

Review Questions 1. Although Methyl Red Test and Voges-Praskauer Test uses the same medium (MR-VP broth) E.coli and E. aerogenes is giving different colors in each test (see the figure below). Please explain the reason. 5 Escherichia coli Enterobacter aerogenes Methyl Red VP Methyl Red VP 2. In the citrate utilization test, indicator bromothymol blue (reactions given below) is used. Degradation of citrate is yielding formation of CO2. Which color do you expect to observe for a positive citrate test result? 5 blank pH 2.1 pH 6.4 pH 6.7 pH 6.9 pH 7.0 pH 7.4 pH 8.1 pH 12.5

Transcript

00:01 Hello everyone, in this question we have been said that although the methyl red test and the woger -prosker test uses the same medium that is mrvp broth, the e.

00:20 Coli and the e.

00:23 Oro genes is giving different colors in each the test.

00:30 So we need to explain the reason for this.

00:34 So here we can see that this methyl red test and woger -prosker test is used to differentiate between the bacterias which are acid forming and the bacterias which are acetone forming.

00:55 So this medium that is the mrvp broth here contains the glucose, the sodium, phosphate, buffer as well as the peptones.

01:09 The methyl red test is used to differentiate the acid forming bacteria.

01:18 So here the bacteria uses the fermentation pathway to ferment the glucose and due to which the breakdown here will produce the acidic product to generate the energy for the utilization of these bacterias.

01:42 And due to this acidic production there will be more protons in the solution and due to which here the ph will decrease.

01:50 So there is the indicator that is methyl red.

01:55 So when the methyl red is added into the medium the methyl red remains red in color.

02:05 This shows that the ph here is low and the medium is acidic and the bacteria has undergone the fermentation process of the glucose and if there is yellow color then this will indicate that there is alkaline ph and the bacteria has used the 2 ,3 -butanidol fermentation pathway.

02:29 So the positive test shows the red color and the negative test shows the yellow color.

02:39 Now if we talk about the burgess prusker test here we will see that this is used to find the acetone forming bacteria and this bacteria do not ferment the glucose rather it undergoes the 2 ,3 -butanidol fermentation.

03:00 So these bacteria ferment the glucose and here the usual pathway does not take place and here acetone is produced.

03:11 So the potassium hydroxide and the alpha -nepthal is used in this vpt test.

03:22 When the bacteria uses this pathway the reagents react with the acetone and due to which the medium color changes to red and if there is no production of acetone then the medium will be red so it will be yellow.

03:41 So here also this is the positive test and the yellow color gives the negative test...

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