Essay by d_naser December 2014

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Danielle Naser

Professor Jennifer Graham

November 5,2014

Lab 5

Phenol-Red Carbohydrate Fermentation Broths


The main purpose for this lab experiment was to distinguish the ability of microorganisms to degrade and ferment carbohydrates with the production of acid and gas. This experiment also helped to understand the differences between cellular respiration and fermentation. Fermentation is a metabolic process performed by almost all types of bacteria. This will result in the production of ATP, the ultimate energy source of the organism. This will happen either in the presence of absence of atmospheric oxygen. The carbohydrate test is used for the fermentation of lactose, sucrose, and dextrose/glucose. Glucose is a sugar that some bacteria can use because of an enzyme that begins the breakdown of this compound. Phenol red glucose (dextrose) broth is used to determine whether the microbe can use the sugar glucose for carbon and energy. When many microbes ferment glucose they produce gases, mainly carbon dioxide and hydrogen.

These gases bubble up through the medium and escape into the atmosphere. Durham tubes serve as gas traps for collecting bubbles generated by gas-producing microbes. The phenol-Red Carbohydrate broth contains Carbohydrate, Phenol-Red, and lastly a Durham tube. The carbohydrate contains a single fermentable carbohydrate. The Phenol-Red is a pH indicator that is red at pH 7 or higher (alkaline) but turns yellow at a low pH (acidic). Lastly, the Durham tube is a small test tube that is inverted (upside-down) in the broth. If gases are produced, they will be trapped in the Durham tube and a gas bubble forms. The organisms used in this experiment consisted of Escherichia Coli, Micrococcus Luteus, Pseudomonas Aeruginosa, and lastly Staphylococcus Aureus.


Organisms used- Escherichia Coli, Micrococcus Luteus, Salmonella thyphimurium, and lastly Staphylococcus Aureus.

4 Phenol-Red Mannitol

4 Phenol-Red Sucrose

4 Phenol-Red...