the Celt olt fs comforea of a thin layer o( P Hadglycar. 14. Urea Agar i. Descri
ID: 217863 • Letter: T
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the Celt olt fs comforea of a thin layer o( P Hadglycar. 14. Urea Agar i. Describe a positive reaction and a negative reaction in Urea test tube test:(4 points) li. What is the indicator in this medium? (2 points... li. What causes the color change? (2 points). iv. Describe the chemical basis of this reaction. (2 points) If any? (2 points) iv. What is the name of the enzyme? v. And what is the substrate? (3 points. 15. Which one of the following gram staining sequences is correct? a. Air dry, decolorize, make smear, heat fix, crystal violet, iodine mordant, safranin, visualize t ootranin heat fix decolorize, visualizeExplanation / Answer
14) i) If an organism able to produce the enzyme urease and hydrolyzes urea, the ammonia is released from the reaction, and that is responsible to cause the pH of the medium to increase. Slow urease-postive reactions will be red, rapid urease-positive reactions will be hot pink (these reactions can occur in 24 hrs). Negative reactions will remain the yellow color.
ii) Phenol Red is the indicator in this medium. It is a pH indicator that is yellow at neutral pH, red at alkaline pH up to 8.2, and hot pink at pH greater than 8.2.
iii) Some bacteria can produce urease that is responsible to hydrolyze urea, and release ammonia and carbon dioxide. Produced ammonia causes the color change.
iv) (NH2)2CO + 2H2O --------? CO2 + H2O + 2 NH3
In presence of urease enzyme, urea is hydrolyzed to release ammonia and carbon dioxide.
v) The name of the enzyme is urease.
vi) The substrate is urea ((NH2)2CO).
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