Question 1

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

Accepted Answer

Selective media inhibit the growth of certain organisms, while differential media allow all organisms to grow but distinguish them based on biochemical reactions.

Question 2

A student prepares a slide for microscopy using the smear preparation procedure. What is the main purpose of heat fixing the smear?

Accepted Answer

To kill the bacteria and adhere them to the slide, preventing them from washing off during staining.

Question 3

You are using a microscope with a 10X ocular lens and a 40X objective lens. What is the total magnification?

Accepted Answer

400X

Question 4

Which of the following is a fomite?

Accepted Answer

A contaminated doorknob that can transmit pathogens.

Question 5

During the Gram stain procedure, which step is responsible for differentiating Gram positive from Gram negative bacteria?

Accepted Answer

Decolorization with alcohol or acetone.

Question 6

Which organism is known to grow and ferment mannitol on MSA (Mannitol Salt Agar)?

Accepted Answer

Staphylococcus aureus

Question 7

A TSI (Triple Sugar Iron) slant is inoculated and after incubation shows a yellow butt, red slant, and gas bubbles. How many sugars have been fermented and what does the gas indicate?

Accepted Answer

One sugar fermented; gas production from fermentation.

Question 8

Which of the following media is both selective and differential for Gram negative rods and uses lactose fermentation as a differential agent?

Accepted Answer

MacConkey agar (MAC)

Question 9

In the catalase test, which reaction indicates a positive result?

Accepted Answer

Formation of bubbles upon addition of hydrogen peroxide ($$2H_2O_2 \rightarrow 2H_2O + O_2$)

Question 10

Which family of organisms does the TSI slant help to differentiate?

Accepted Answer

Enterobacteriaceae

Question 11

A student observes a culture growing only at the top of a thioglycollate broth tube. What is the aerotolerance classification of this organism?

Accepted Answer

Obligate aerobe

Question 12

Which reagent is used in the oxidase test to detect the presence of cytochrome c oxidase?

Accepted Answer

Tetramethyl-p-phenylenediamine

Question 13

Which of the following best describes the purpose of aseptic technique in microbiology?

Accepted Answer

To prevent contamination of cultures and the environment by unwanted microorganisms.

Question 14

Which pH indicator is commonly used in carbohydrate fermentation broth to detect acid production?

Accepted Answer

Phenol red

Question 15

A student performs a nitrate reduction test and observes no color change after adding nitrate reagents, but a red color appears after adding zinc powder. What does this result indicate?

Accepted Answer

Nitrate was not reduced by the organism.

Question 16

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

Accepted Answer

The environment has a higher solute concentration than the cell, causing water to leave the cell.

Question 17

Which flagellar arrangement describes a bacterium with a single flagellum at one end?

Accepted Answer

Monotrichous

Question 18

Which group of organisms is inhibited by the agents in EMB and MAC plates?

Accepted Answer

Gram positive bacteria

Question 19

A blood agar plate is used to test for hemolysis. Which type of hemolysis is characterized by a clear zone around colonies?

Accepted Answer

Beta hemolysis

Question 20

Which step in the Schaeffer-Fulton spore stain procedure is responsible for staining the spores?

Accepted Answer

Application of malachite green with heat

Microbiology Lab Midterm Review Guidance

Guida di studio - Domande di pratica

Study guide - Flashcard