The Methyl red test is used as a PH indicator test. This is done through identifying enteric bacteria that generate stable acids through means of combined fermentation of glucose, dependent on their style of glucose metabolism. The test is performed by adding five drops of Methyl Red PH indicator to the prepared test tube. A positive test turns red indicating PH that is lower than 4.41.
The Voges-Proskauer test distinguishes which organisms exploit the butylene glycol pathway and also create acetoin. Completion of the Voges-Proskauer test is dependent upon consumption of glucose which releases acetoin (acetymethylcarbinol). As the glucose ferments it also produces 2,3-butanediol. The test is executed by adding alpha-naphtol and potassium hydroxide to the MR-VP broth with the bacteria already in the broth. A positive result is evidenced by a cherry-red colored result2.
Organisms that ferment glucose:
E. coli ferments glucose, S. Epidermidis does not ferment glucose Organisms producing acid byproducts:
S. Epidermidis produces acetoin. E. coli produces various acid by products however, does not produce acetoin. Different biochemical pathways:
Glucose is mainly metabolized by the 10-step pathway called glycolysis (glycolytic). Other pathways include glycogenesis, Enter-Doudoroff, Oxidative pentose phosphate, Hetrotrophic, and finally fermentation. The end result of each and every pathway is the production of pyruvate. Each organism must have a different biochemical pathway. A biochemical pathway has to be able to metabolize glucose. A reason that there are different pathways is simply that there are different environments. A pathway designed for an oxygenate environment, while not be able to metabolize glucose in a non-oxygenated environment. Therefore the organisms had to adapt their metabolic pathways to adapt to the environment that they are in3.