V. Citrate fermentation Examine both tubes and look for a blue color to indicate
ID: 3516834 • Letter: V
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V. Citrate fermentation Examine both tubes and look for a blue color to indicate that the organism was able to ferment citrate. Keep in mind that the medium contains ammonium salts that the species uses to produce ammonia as a waste product. The ammonia raises the pH and turns the indicator from green to blue Unknowrn Color change after incubation Enterobacter blue Oxidation tests Cytochrome C oxidase test. Use the artificial electron acceptor to detect the presence of the cytochrome C. Use a sterile swab to grab a little of the pseudomonas from the TSA plate you streaked last week. Add drops of the artificial acceptor and C. Do the same for the unknown. look for a purple color change to indicate the presence of cytochrome Unknown Pseudomonas Color after addition of artificial electron acceptor purple Il. Catalase test. Obtain 2 slides and label one unknown and the other S. aureus. Using a sterile loop, place a small sample of the species onto the slide and add a couple of drops of hydrogen peroxide. Look for the formation of bubbles to indicate the presence of catalase. The catalase will break down the peroxide into water and oxygen gas. Unknown S. aureus Yes! Presence of bubbles after the addition of hydrogen peroxide? Nitrate reduction You will need to add drops of Nitrate Reagent A and nitrate reagent B to both tubes. A red color indicated a positive reaction. IlI. Unknown E.coli red Color after addition of reagent A and reagent BExplanation / Answer
Citrate fermentation
The citrate test detects the ability of an organism to use citrate as the sole source of carbon and energy.
Bacteria are inoculated on a medium containing sodium citrate and a pH indicator like bromothymol blue. The medium also contains inorganic ammonium salts which are utilized as sole source of nitrogen.
Use of citrate involves the enzyme citrase which breaks down citrate to oxaloacetate and acetate. Oxaloacetate is further broken down to pyruvate and carbon dioxide.
Production of sodium bicarbonate as well as ammonia from the use of sodium citrate and ammonium salts results in alkaline pH. This results in a change in medium's colour from green to blue.
If the organism has the ability to use citrate, the medium colour changes from green to blue.
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