9. Microscopes

Which of the following answers lists the steps of gram-staining in the correct order?

Which of the following reagents is used to stain gram negative cells pink (or red) in the gram stain?

Which of the following statements is false?

Results from a gram stain show that these bacteria are:

A scientists has a sample with two different species of bacteria. The first species is Staphylococcus aureus, a gram-positive bacterium. The second species is Escherichia coli, a gram-negative bacterium. The scientist gram-stains his sample of bacteria. What colors will the two species of bacteria be after staining?

Why is a mordant used in the Gram stain? In the flagella stain?

What is the purpose of a decolorizer in the Gram stain? In the acid-fast stain?

Which of the following pairs is mismatched?

a. Capsule—negative stain

b. Cell arrangement—simple stain

c. Cell size—negative stain

d. Gram stain—bacterial identification

e. None of the above

Fill in the following table regarding the Gram stain:

Carbolfuchsin can be used as a simple stain and a negative stain. As a simple stain, the pH is:

a. 2

b. Higher than the negative stain

c. Lower than the negative stain

d. The same as the negative stain

Assume that you are viewing a Gram-stained field of red cocci and blue rods through the microscope. You can safely conclude that you have

a. Made a mistake in staining

b. Two different species

c. Old bacterial cells

d. Young bacterial cells

e. None of the above

Why is it clinically helpful to know the Gram property of an organism?

Indicate the true statements and then correct the false statements so that they are true.

a. The Gram stain is a simple stain.

b. Simple stains reveal information about size, shape, and arrangement.

c. Bright field microscopy requires a stained sample.

d. Dark field microscopy requires a stained sample.

e. The acid-fast stain detects peptidoglycan in the cell walls of certain bacteria.

f. Gram-positive bacteria have a thin peptidoglycan layer in the cell wall.

Select the most accurate statement.

a. The Gram stain is a simple stain.

b. Bacterial endospores appear green from the acid-fast stain.

c. The acid-fast stain is used to detect bacteria that have a capsule.

d. Bacterial flagella can only be seen with electron microscopes.

e. The mordant in the Gram stain is iodine.

Explain why Gram-positive mycoplasmas appear pink in a Gram-stained smear.