Question 1

Which of the following best describes the primary use of an agar slant in microbiology laboratories?

Accepted Answer

To maintain stock cultures for long-term storage

Question 2

A microbiologist wants to differentiate between Staphylococcus and Streptococcus species using a rapid biochemical test. Which test should be performed and what result would indicate Staphylococcus?

Accepted Answer

Catalase test; bubbling upon addition of $$H_2O_2$$

Question 3

Which of the following media is both selective and differential, and is used to isolate and differentiate members of the Enterobacteriaceae based on their ability to ferment lactose?

Accepted Answer

MacConkey agar

Question 4

A bacterial culture is inoculated into a tube of phenol red broth containing glucose. After incubation, the broth turns yellow and a bubble is present in the Durham tube. What does this indicate?

Accepted Answer

The organism ferments glucose and produces gas

Question 5

Which of the following best explains why agarose gel concentration affects DNA migration during electrophoresis?

Accepted Answer

Lower agarose concentration increases pore size, allowing larger DNA fragments to move farther

Question 6

A microbiologist observes a blood agar plate with a clear, colorless zone around the bacterial colonies. Which type of hemolysis is this, and which organism is most likely responsible?

Accepted Answer

Beta hemolysis; Streptococcus pyogenes

Question 7

Which of the following equations correctly represents the catalase reaction?

Accepted Answer

$$2H_2O_2 \xrightarrow{catalase} 2H_2O + O_2$

Question 8

A bacterium is inoculated into a Triple Sugar Iron Agar (TSIA) slant. After incubation, the slant is red and the butt is yellow. What does this result indicate?

Accepted Answer

Fermentation of glucose only

Question 9

Which of the following best describes the function of TBE buffer in DNA electrophoresis?

Accepted Answer

It maintains pH and provides high buffering capacity for sharp DNA band resolution

Question 10

A microbiologist is testing an unknown bacterium for its ability to reduce nitrate. After adding nitrate reagents A and B, the broth remains clear. After adding zinc, the broth turns red. What is the correct interpretation?

Accepted Answer

Nitrate was not reduced by the organism

Question 11

Which of the following best describes the difference between selective and differential media?

Accepted Answer

Selective media inhibits the growth of some organisms, while differential media distinguishes between two different microbes

Question 12

Which of the following organisms is a facultative anaerobe and can grow in both the presence and absence of oxygen?

Accepted Answer

Escherichia coli

Question 13

A microbiologist observes a metallic green sheen on Eosin Methylene Blue (EMB) agar. Which organism is most likely responsible for this result?

Accepted Answer

Escherichia coli

Question 14

Which of the following best describes the effect of a hypertonic environment on bacterial cells?

Accepted Answer

Water leaves the cell, causing plasmolysis

Question 15

Which of the following is true regarding the use of phenol red as a pH indicator in fermentation tests?

Accepted Answer

Phenol red turns yellow at pH below 6.8

Question 16

Which of the following best explains why water cannot be used as a substitute for buffer in DNA electrophoresis?

Accepted Answer

Water would cause little to no DNA migration, overheating, and potential DNA damage

Question 17

A microbiologist is using a spectrophotometer to estimate bacterial growth in a broth culture. Which of the following statements is correct?

Accepted Answer

Higher absorbance indicates more bacterial cells

Question 18

Which of the following best describes the purpose of the oxidase test in bacterial identification?

Accepted Answer

To detect the presence of cytochrome c oxidase enzyme

Question 19

Which of the following best describes the result of a facultative halophile growing on a medium containing 7.5% NaCl?

Accepted Answer

Growth will occur in both low and high salt concentrations

Question 20

Which of the following is the correct formula for calculating total magnification when using a microscope?

Accepted Answer

$$	ext{Total magnification} = 	ext{Objective magnification} 	imes 	ext{Ocular magnification}$$

Microbiology Study Notes: Media Types, Staining, and Selective/Differential Agar

Study Guide - Practice Questions

Study Guide - Flashcards