Q: Which of the following equations correctly represents the decarboxylation of an amino acid by a decarboxylase enzyme?

$$\mathrm{R-CH(NH_2$)-COOH} \xrightarrow{\text{decarboxylase}} \mathrm{R-CH_2$-NH_2$} + CO_2$

Q: Which reaction is detected in the phenylalanine deaminase test?

$$\text{Phenylalanine} \xrightarrow{\text{deaminase}} \text{Phenylpyruvic acid} + NH_3$

Question 1

Which of the following best describes the principle behind the oxidase test using TMPD as shown in the first image?

Accepted Answer

TMPD acts as an electron donor to cytochrome c oxidase, and when oxidized, it develops a blue color.

Question 2

In the DrySlide oxidase test (second image), what does the blue color in window B indicate about the bacterial sample?

Accepted Answer

The bacteria possess cytochrome c oxidase and can oxidize TMPD.

Question 3

Which family of bacteria is typically oxidase negative and can be differentiated from oxidase positive Pseudomonadaceae using the oxidase test?

Accepted Answer

Enterobacteriaceae

Question 4

Refer to the electron transport chain diagram (third image). Which enzyme is responsible for reducing nitrate ($$NO_3$$^-$$) to nitrite (NO_2$^-) $$during anaerobic respiration?

Accepted Answer

Nitrate reductase

Question 5

Based on the nitrogen reduction pathway (fourth image), how many electrons are required to reduce nitrate ($$NO_3$$^-$$) to ammonium (NH_4$^+$$)?

Accepted Answer

$$8e^-$$

Question 6

In the nitrate reduction test, what does a red color after adding reagents A and B indicate?

Accepted Answer

Nitrate has been reduced to nitrite ($$NO_2$$^-$$).

Question 7

If no color change occurs after adding nitrate reagents A and B, but a red color appears after adding zinc, what does this indicate?

Accepted Answer

Nitrate was not reduced by the bacteria.

Question 8

Which of the following equations correctly represents the decarboxylation of an amino acid by a decarboxylase enzyme?

Accepted Answer

$$\mathrm{R-CH(NH_2$)-COOH} \xrightarrow{	ext{decarboxylase}} \mathrm{R-CH_2$-NH_2$} + CO_2$

Question 9

In the citrate utilization test, what does a blue color indicate about the organism?

Accepted Answer

The organism can utilize citrate as a sole carbon source, producing alkaline byproducts.

Question 10

Which of the following best explains why mineral oil is added to the top of the medium in a decarboxylase test?

Accepted Answer

To create an anaerobic environment that promotes glucose fermentation and acid production.

Question 11

A decarboxylase test tube turns purple after incubation. What does this result indicate?

Accepted Answer

The organism decarboxylated the amino acid, producing alkaline amines.

Question 12

Which reaction is detected in the phenylalanine deaminase test?

Accepted Answer

$$	ext{Phenylalanine} \xrightarrow{	ext{deaminase}} 	ext{Phenylpyruvic acid} + NH_3$

Question 13

After adding ferric chloride ($$FeCl_3) to a $$phenylalanine deaminase test, a green color develops. What does this indicate?

Accepted Answer

Phenylpyruvic acid is present, indicating phenylalanine deamination.

Question 14

Which of the following is a correct sequence of steps for interpreting a nitrate reduction test?

Accepted Answer

Add reagents A and B, observe for red color; if no color, add zinc; red after zinc means no reduction.

Question 15

Which of the following best explains why a bacterium that reduces nitrate all the way to nitrogen gas ($$N_2) $$will not turn red after the addition of nitrate reagents A and B or zinc?

Accepted Answer

All nitrate has been reduced beyond nitrite, so there is no nitrite or nitrate left to react.

Question 16

Which of the following is a real-world application of the phenylalanine deaminase test?

Accepted Answer

Differentiating Proteus species from other Enterobacteriaceae in clinical diagnostics.

Question 17

A student performs a citrate test and observes a blue slant after incubation. Which of the following best explains the metabolic process occurring?

Accepted Answer

The organism uses citrate as a carbon source, producing ammonia and raising the pH.

Question 18

Which of the following best describes the role of bromocresol purple in the decarboxylase test?

Accepted Answer

It acts as a pH indicator, turning yellow in acid and purple in alkaline conditions.

Question 19

Which of the following is the correct chemical equation for the reaction detected by the nitrate reduction test?

Accepted Answer

$$NO_3^- + 2e^- + 2H$$^+ \rightarrow $$NO_2^- + H_2O$

Biochemical Testing in Microbiology: Reduction Potential and Nutrient Utilization

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