Question 1

Which metabolic property is specifically tested by the Phenol Red Broth medium?

Accepted Answer

Lactose fermentation

Question 2

What is the role of the Durham tube in the Phenol Red Broth test?

Accepted Answer

It detects the production of CO$_2$ gas.

Question 3

If a bacterium ferments lactose in Phenol Red Broth, what color change is expected in the medium?

Accepted Answer

The medium turns yellow.

Question 4

A student observes a yellow color in the Phenol Red Broth and an air bubble in the Durham tube. What does this indicate about the metabolic activity of the microorganism?

Accepted Answer

Lactose fermentation with CO$_2$ production

Question 5

Which substrate in the Phenol Red Broth is responsible for detecting lactose fermentation?

Accepted Answer

Lactose

Question 6

What does a pink coloration in the Phenol Red Broth indicate?

Accepted Answer

Peptone degradation

Question 7

Which of the following best describes a negative result in the Phenol Red Broth test?

Accepted Answer

No color change and no air bubble in Durham tube

Question 8

Why is phenol red used in the Phenol Red Broth test?

Accepted Answer

It serves as a pH indicator to detect acid production.

Question 9

A microbiologist inoculates Phenol Red Broth with a bacterium. After incubation, the broth is pink and there is no bubble in the Durham tube. What is the most likely explanation?

Accepted Answer

Peptone degradation without gas production

Question 10

Does the Phenol Red Broth test require the addition of reagents after incubation to interpret the results?

Accepted Answer

No, results are visible without additional reagents

Question 11

Which of the following equations best represents the fermentation of lactose by bacteria in the Phenol Red Broth test?

Accepted Answer

$\mathrm{C_{12}H_{22}O_{11} + H_2O \rightarrow 4 CH_3COOH + 4 H_2O + 4 CO_2}$

Question 12

A clinical isolate is tested in Phenol Red Broth. The tube turns yellow, but no bubble is observed in the Durham tube. What does this result suggest?

Accepted Answer

Lactose fermentation without CO$_2$ production

Question 13

Which of the following best explains why the Phenol Red Broth test is considered a differential medium?

Accepted Answer

It distinguishes bacteria based on their ability to ferment lactose.

Question 14

If a bacterium degrades peptone in the Phenol Red Broth, what is the expected pH change and color of the medium?

Accepted Answer

pH increases, medium turns pink

Question 15

Which of the following is NOT a possible result in the Phenol Red Broth test?

Accepted Answer

Blue color with air bubble

Question 16

A student sets up a Phenol Red Broth test and observes no color change and no air bubble after incubation. What is the most likely conclusion?

Accepted Answer

No metabolic activity occurred

Question 17

Which indicator is used in the Phenol Red Broth test to detect acid production from lactose fermentation?

Accepted Answer

Phenol red

Question 18

In a real-world scenario, why might a physician request a Phenol Red Broth test for a clinical isolate?

Accepted Answer

To determine the isolate's ability to ferment lactose, aiding in identification

Question 19

Which of the following best describes the chemical reaction that leads to a yellow color in the Phenol Red Broth?

Accepted Answer

Production of acidic byproducts from lactose fermentation

Question 20

A microbiology student is asked to interpret the results of a Phenol Red Broth test. The tube is yellow and contains an air bubble in the Durham tube. Which of the following equations best represents the metabolic process that occurred?

Accepted Answer

$\mathrm{C_{12}H_{22}O_{11} + H_2O \rightarrow 4 CH_3COOH + 4 CO_2}$

Phenol Red Broth: Differential Medium for Lactose Fermentation

Study Guide - Practice Questions

Study Guide - Flashcards