Microbiology Lab: Methyl Red and Voges-Proskauer Test

Methyl Red and Voges-Proskauer Test
The Methyl Red test shows which bacteria are creating stable acids through mixed acid fermentation of glucose. This helps to identify enteric bacteria by examining how they metabolise glucose. Every enteric bacteria first produces pyruvic acid from metabolism of glucose. A methyl red positive enteric bacteria, uses the mixed acid pathway when breaking down pyruvic acid to different acids, like lactic, acetic, and formic acids. The Voges-Proskauer test determines if there is acetoin found in a bacterial culture. Using alpha-naphthol and potassium hydroxide detects if there is acetoin in the culture. The test is determined by the digestion of glucose to acetylmethylcarbinol. The test will react with alpha-naphthol and potassium hydroxide if glucose is being broken down and turn a red color. If a test is positive it will show a maroon colored band on the top portion of the broth. Lab Results E. coli is MR+ because it does ferment glucose and the has a high acidity produced during the fermentation. E Coli is VP- because it does not make acetyl methyl carbinol, a neutral product. E. Coli produces more acidic products S. epidermidis is MR+ and is VP+ because it first changes to acidic products then is able to convert those acidic products into some neutral basic products so it gives both positive results. Organisms and Metabolism Organisms possess different biochemical pathways to metabolize glucose due to the range of different environments glucose metabolism is needed to occur in. With a low oxygen concentration, it isn’t beneficial to have an oxygen-only glycolysis pathway. With no oxygen at all, a similar problem can occur. Without varied methods for glycolysis to occur, there would be an inability to produce energy or ATP for the cells.

References
Methyl red. (2014, March 16). Retrieved March 21, 2014, from http://en.wikipedia.org/wiki/Methyl_red
Voges-proskauer reaction. (2014). Retrieved March 21, 2014, from http://www.merriam-webster.com/medical/voges-proskauer%2520reaction

References: Methyl red. (2014, March 16). Retrieved March 21, 2014, from http://en.wikipedia.org/wiki/Methyl_red Voges-proskauer reaction. (2014). Retrieved March 21, 2014, from http://www.merriam-webster.com/medical/voges-proskauer%2520reaction