Question

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In a urea broth test, a bacterial species is tested positively. This bacterium must be able to: Select one: O a. absorb urea as a main source of nitrogen and carbon O b. turn the urea broth from red to bright yellow (acidic). O c. release urease as an exoenzyme. O d. digest proteins and release urea as a waste product. Which of these tests is positive før H2S and which is positive for Indole? Select one: O a. right is positive for H2S and left is positive for Indole O b. left is positive for H2S and right is positive for indole O c. Both tests are positive for H2S O d. Both tests are positive for Indole For a positive Urea Broth test Select one: O a ammonia increases the pH Ob color change from orange to pink indicates urea hydrolysis c. the pH level is above 8.4 d. All of the answers are correct

Answer 1

1) The correct answer is-

C- release urease as an exoenzyme

This is because urea test shows ability of an organism to produce an exoenzyme, called urease, that hydrolyzes urea to ammonia and carbon dioxide.

2) The correct answer is-

B- left is positive for H2S and right is positive for indole.

This is because bacteria that have the enzyme tryptophanase which converts the amino acid, tryptophane to indole. Indole reacts with added Kovac's reagent to form rosindole dye which is red in color.

The H2S positive test produce blue black solution.

3) The correct answer is-

D- all of the above are correct.

This is because hydrolysis of urea by urease producing bacteria leads to produce ammonia and CO2. The formation of ammonia alkalinizes the medium, and the pH shift is detected by the color change of phenol red from light orange at pH 6.8 to magenta (pink) at pH 8.1.