Question 1

Which step in the Gram staining procedure is most critical for differentiating between Gram-positive and Gram-negative bacteria?

Accepted Answer

Decolorization with ethanol or acetone

Question 2

A student performs a Gram stain but forgets to apply the iodine. What is the most likely result?

Accepted Answer

Both Gram-positive and Gram-negative cells will appear pink

Question 3

Why is heat fixing necessary before staining bacterial smears?

Accepted Answer

It kills the bacteria and adheres them to the slide

Question 4

Which equation best represents the relationship between the concentration of stain and the intensity of color observed in a bacterial smear?

Accepted Answer

$$I = k 	imes C$$

Question 5

In acid-fast staining, which property of Mycobacterium species allows them to retain the primary stain after decolorization?

Accepted Answer

High lipid content in the cell wall

Question 6

A clinical sample is stained using the acid-fast technique. If the cells appear blue, what does this indicate?

Accepted Answer

The cells are acid-fast negative

Question 7

Which of the following is NOT a structural stain used in microbiology?

Accepted Answer

Gram stain

Question 8

During the endospore staining procedure, what is the purpose of heating the slide with malachite green?

Accepted Answer

To allow the stain to penetrate the endospore

Question 9

Which formula would you use to calculate the dilution factor when preparing a bacterial smear?

Accepted Answer

$$DF = \frac{V_{total}}{V_{sample}}$$

Question 10

A microbiologist observes a slide stained for flagella and sees multiple flagella at one end of the cell. What is the correct term for this arrangement?

Accepted Answer

Lophotrichous

Question 11

Which step in the capsule staining procedure is essential to avoid destroying the capsule?

Accepted Answer

Air drying the smear

Question 12

If a bacterial cell is observed to be acid-fast positive, which disease is it most likely associated with?

Accepted Answer

Tuberculosis

Question 13

Which of the following best describes the principle behind the flagella stain?

Accepted Answer

Stain increases the diameter of flagella for visibility

Question 14

A student is asked to identify a bacterium using Gram stain, acid-fast stain, and endospore stain. Which sequence of stains would best differentiate Bacillus from Mycobacterium?

Accepted Answer

Gram stain, acid-fast stain, endospore stain

Question 15

Which equation would you use to estimate the number of bacteria per field of view after staining?

Accepted Answer

$$N = \frac{A_{field}}{A_{cell}}$$

Question 16

Which of the following is a common error that leads to false Gram-negative results in Gram-positive bacteria?

Accepted Answer

Over-decolorization with ethanol

Question 17

In the capsule staining procedure, what is the appearance of the capsule under the microscope?

Accepted Answer

Capsule appears colorless against a stained background

Question 18

Which of the following stains is used to visualize endospores?

Accepted Answer

Malachite green

Question 19

A sample is stained and observed to have red cells with green oval structures inside. What does this indicate?

Accepted Answer

Endospore-forming bacteria

Question 20

Which step is shared by both Gram staining and acid-fast staining procedures?

Accepted Answer

Application of a primary stain

Microbiology Study Guide: Staining Techniques and Microbial Morphology

Study Guide - Practice Questions

Study Guide - Flashcards