Question 1

Which enzyme is detected by adding iodine to a starch agar plate and observing a clear zone around bacterial growth?

Accepted Answer

Amylase

Question 2

A microbiologist observes a clear zone on a skim milk agar plate after incubation. Which enzyme is responsible for this result, and what substrate is being degraded?

Accepted Answer

Protease; casein protein

Question 3

On a spirit blue agar plate, a dark blue precipitation is observed around bacterial colonies. What does this indicate about the organism?

Accepted Answer

It produces lipase and releases fatty acids

Question 4

A student adds Kovac's reagent to a tryptone broth and observes a red ring at the top. What does this result indicate?

Accepted Answer

The organism produces tryptophanase and breaks down tryptophan to indole

Question 5

Which of the following best describes the chemical reaction catalyzed by urease in the urea agar slant test?

Accepted Answer

$$\mathrm{CO(NH_2$)_2 + H_2O \rightarrow 2NH_3 + CO_2$}$$

Question 6

After adding 10% ferric chloride to a phenylalanine agar slant, a greenish color develops. What does this indicate?

Accepted Answer

The organism produces phenylalanine deaminase, converting phenylalanine to phenylpyruvic acid

Question 7

Kligler’s Iron Agar is used to test for which of the following bacterial properties? Select the most complete answer.

Accepted Answer

Glucose fermentation, lactose fermentation, and hydrogen sulfide production

Question 8

A tube of SIM medium is inoculated and after incubation, a black precipitate forms along the stab line. What does this result indicate?

Accepted Answer

The organism produces hydrogen sulfide from cysteine breakdown

Question 9

Which of the following best explains why SIM medium is considered semi-solid and what property it allows you to test?

Accepted Answer

It contains 0.7% agar, allowing detection of motility

Question 10

In the litmus milk test, which observation would indicate fermentation of lactose by the organism?

Accepted Answer

A pink color change

Question 11

A microbiologist is testing an unknown bacterium. The organism produces a clear zone on starch agar after iodine is added, a clear zone on skim milk agar, and a blue precipitate on spirit blue agar. Which enzymes are likely produced by this organism?

Accepted Answer

Amylase, protease, and lipase

Question 12

Which of the following is a correct interpretation of a bright pink color in a urea agar slant after incubation?

Accepted Answer

The organism produces urease, which hydrolyzes urea to ammonia, raising the pH

Question 13

Why are multiple testing media such as Kligler’s Iron Agar and SIM considered advantageous in bacterial identification?

Accepted Answer

They allow detection of several metabolic properties in a single test, saving time and resources

Question 14

A student inoculates a SIM tube and after incubation, observes a red ring after adding Kovac’s reagent and a diffuse growth away from the stab line. What two properties can be concluded about the organism?

Accepted Answer

It is motile and produces indole

Question 15

Which of the following best describes the reaction detected in the phenylalanine deaminase test?

Accepted Answer

$$\mathrm{C_9H_{11}NO_2$ + O_2$ \rightarrow C_9H_8O_3 + NH_3$}$$

Question 16

During a litmus milk test, the medium turns white. What is the most likely explanation for this observation?

Accepted Answer

Litmus reduction due to a drop in oxygen, causing the dye to become reduced

Question 17

Which of the following is the correct sequence of steps for detecting indole production in a SIM or tryptone broth?

Accepted Answer

Inoculate medium, incubate, add Kovac’s reagent, observe red ring

Question 18

A bacterium is inoculated into Kligler’s Iron Agar. After incubation, the butt of the tube is yellow and the slant is red. What does this result indicate?

Accepted Answer

Glucose fermentation only

Question 19

Which of the following best explains why a blue color develops in litmus milk after incubation?

Accepted Answer

Breakdown of proteins leads to ammonia formation, raising the pH

Identifying Bacteria Based on Enzymatic Activity and Differential Media

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