Task 5 A. Explain what the methyl red test determines. Methyl red test is used to determine whether bacteria can perform mixed-acid fermentations when supplied with glucose (Ramakrishnan, & Sulochana, 2012). Methyl red test shows positive when the culture medium turns red after methyl red is added, because of a pH level of 4.4 or below from the fermentation of glucose. On the other hand, methyl red test is negative when the culture medium remains yellow, which occurs when little acid is produced due to the glucose being fermented i.e. high pH level of 6.0 or above. B. Explain what the Voges-Proskauer test determines. Voges-Proskauer test is used to identify enteric bacteria based on how they metabolize glucose. The enteric bacteria’s that produce neutral end-products, such as acetoin are detected by VP test (Ramakrishnan, & Sulochana, 2012). Positive test: acetoin + alpha-naphthol + KOH = red color. Negative test: alpha-naphthol +KOH = copper color (Ramakrishnan, & Sulochana, 2012). C. Discuss which of your organisms, if any, fermented glucose. S. epidermidis came out positive for glucose fermentation. D. Discuss which of your organisms, if any, produced measurable acidic by-products. Escherichia coli and s. epidermidis was tested and produced measurable acidic by-products from the experiment performed. E. Explain why organisms would have different biochemical pathways to metabolize glucose.
Microbes are often identified using biochemical tests that detect specific enzymes of metabolic pathways. E. coli typically ferments lactose. It produce pyruvic acid initially from glucose metabolism. Some microbes use the mixed acid pathway to metabolize pyruvic acid to other acids (Ramakrishnan, & Sulochana, 2012).