Question

Timed Test This test has a time limit of 1 hour and 35 minutes. You will be notified when time expires, and you may continue or submit Warnings appear when half the time, 5 minutes, 1 minute, and 30 seconds remain Not allowed. This test can only be taken once. Multiple Attempts Force Completion Once started, this test must be completed in one sitting. Do not leave the test before clicking Save and Submit. This test does not allow backtracking. Changes to the answer after submission are prohibited. Remaining Time: 1 hour, 24 minutes, 10 seconds. * Question Completion Status: A Moving to the next question prevents changes to this answer. Question 20 of 36 3! Question 20 3 points Save Answer Which organism turns the SIM and TSIA tubes produce a black precipitate consisting of FeS2 (and can cause the colonies on Hektoen agar to turn black)? O a. Pseudomonas aeruginosa b. Proteus vulgaris Micrococcus luteus Ос. d. E. coli

Answer 1

TSIA ( triple sugar iron agar) is a medium containing the carbohydrates glucose, lactose, and sucrose, and iron salts.

Here ferrous ammonium sulfate serves as the indicator, which turns the butt black in the presence of free hydrogen sulfide gas.

Enteric organisms that are capable of fermenting glucose along with a positive hydrogen sulfide result.

Among the given options E coli , Proteus vulgaris and pseudomonas aeroginosa are enteric organisms.

Hektoen agar - here the H2S gas reacts with the ferric ammonium citrate, forming a precipitate, resulting in colonies that are black. Some non pathogenic enteric organisms, such as Proteus species produces black centers.

Hence the answer is:

Proteus vulgaris