Methyl Red and Voges-Proskauer Tests (MR-VP) PDF

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Summary

Using MR-VP method to learn about fermentation pathway in bacteria....

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Methyl Red and Voges-Proskauer Tests (MR-VP) Purpose: Using MR-VP method to learn about fermentation pathway in bacteria. Materials:  

MR-VP broth Methyl red and Barritt’s reagents (A & B) • Cultures  Escherichia coli (positive for MR; negative for VP)  Enterobacter aerogenes (positive for VP; negative for MR)

Methods: Refer to page 71 in the BIOL302 Lab manual. The lab was conducted by the instructor, and result were given Results:

A

B

Figure 1: Bacterial cultures (A) Escherichia coli (B) Enterobacter aerogenes were placed in an incubator that automatically shook the tubes, to oxygenated them They were incubated at 37 degree and oxygenated for 48 hours. After that MR-VP method used to test the tubes with.

Discussion: MR-VP broth contains dextrose. It is used to identify the pathway the organisms use for fermentation. Using Methyl Red (MR), bacteria fermentation of dextrose, will result in acidification and if it PH goes below 5, then the media color change to red. This pathway is called mixed acid fermentation. MR method is not useful in organisms that produce alcohol instead of acid, since alcohol does not affect the PH. In this case, Voges-Proskaur(VR) method can be used to detect pathway of organisms that ferment dextrose to alcohol (butanediol) and measure acetonin. Media will change to pink or red color if acetonin is produced. Figure 1 shows that the bacteria gave a positive response to MR test. However, it gave a negative response to VR. This means that that specific bacteria pathway was mixed acid fermentation. Figure 1B, shows E. aerogenes gave a negative response to MR test (no change in color), and instead gave a positive response to VR (pink/red color). This is an indication that this bacteria pathway lead alcohol fermentation.

Questions: NONE...