Question 1

Which of the following is a routinely used method, other than staining, to identify and differentiate bacteria in the laboratory?

Accepted Answer

Biochemical testing using differential media

Question 2

Which type of media is most commonly used for biochemical testing of bacteria?

Accepted Answer

Differential media

Question 3

Why are enzymes critical in biochemical testing for bacterial identification?

Accepted Answer

They catalyze specific reactions that can be detected by changes in the media

Question 4

Amylase is an enzyme involved in starch hydrolysis. Which statement best describes amylase?

Accepted Answer

It is an exoenzyme that breaks down starch outside the cell

Question 5

A microbiologist wants to test for amylase production by a bacterial isolate. Which of the following steps is correct?

Accepted Answer

Add iodine to the starch agar after bacterial growth to observe a color change

Question 6

What color reaction indicates a positive starch hydrolysis test after adding iodine to the plate?

Accepted Answer

A clear zone around the colony

Question 7

The hydrolysis of protein by bacteria is called proteolysis. Which enzyme is primarily responsible for this process?

Accepted Answer

Protease

Question 8

Which medium is commonly used to detect proteolysis by bacteria?

Accepted Answer

Skim milk agar

Question 9

A clear zone around bacterial growth on a skim milk agar plate indicates:

Accepted Answer

The bacteria produce protease and hydrolyze casein

Question 10

Which of the following best describes the two main ways bacteria produce energy from carbohydrates?

Accepted Answer

Fermentation and aerobic respiration

Question 11

Which type of organism is most likely to exhibit fermentation as a means of energy production?

Accepted Answer

Facultative anaerobes

Question 12

What are the two main end products of carbohydrate fermentation in bacteria?

Accepted Answer

Acid and gas

Question 13

A carbohydrate fermentation tube contains a Durham tube and phenol red. What result would you expect if the bacteria ferment the carbohydrate?

Accepted Answer

The medium turns yellow and a gas bubble forms in the Durham tube

Question 14

In a carbohydrate fermentation test, what does a red color in the medium after incubation indicate?

Accepted Answer

The bacteria did not ferment the carbohydrate

Question 15

SIM medium is used to detect which of the following bacterial activities?

Accepted Answer

Sulfur reduction, indole production, and motility

Question 16

How is hydrogen sulfide ($$\mathrm{H_2S}) $$production detected in SIM medium?

Accepted Answer

By the appearance of a black precipitate in the medium

Question 17

Why is the SIM medium stabbed with an inoculating needle when testing for $$\mathrm{H_2S}$$ production?

Accepted Answer

To allow detection of motility and anaerobic reactions

Question 18

What is the role of iron salts in SIM medium for detecting $$\mathrm{H_2S}$$ production?

Accepted Answer

They react with $$\mathrm{H_2S} to $$form a black precipitate of iron sulfide ($$\mathrm{FeS})$$

Question 19

Indole production in bacteria is detected using which reagent, and what is a positive result?

Accepted Answer

Kovac's reagent; a red ring at the top of the tube

Question 20

Which enzyme is produced by indole-positive bacteria, and what substrate does it act on?

Accepted Answer

Tryptophanase; tryptophan

Question 21

Catalase protects bacterial cells by catalyzing which reaction?

Accepted Answer

$$2\mathrm{H_2O_2} \rightarrow 2\mathrm{H_2O} + \mathrm{O_2$}$$

Microbiology Lab Biochemical Testing Study Guide – Step-by-Step Guidance

Study Guide - Practice Questions