Group 2 - Chapter 03: Section 3.3 - Observing Microorganisms Through a Microscope

Which of the following staining procedures is correctly matched with the principal use for that particular stain?

Endospore stain to distinguish dormant structures formed during adverse environmental conditions

Which of the following steps is common to both the Gram stain and the acid-fast stain?

Heat fixation of the smear before staining

Your lab partner tells you the bacteria are moving in his Gram-stained smear. You can conclude that __________.

he didn't properly fix the smear

In the Gram stain, crystal violet remains in gram-positive cells after treatment with alcohol because crystal violet--iodine (CV--I) complexes are trapped __________.

in thick layers of peptidoglycan

__________ is an example of an acidic dye; __________ is an example of a basic dye.

nigrosin; crystal violet

In the Gram stain, what is the purpose of the counterstain?

To make gram-negative cells visible

In the Gram stain, what is the purpose of the decolorizer?

To selectively remove stain from cells

Bacterial cells have an overall negative charge on their surface. If a bacterial smear is stained by a pink, acidic, water-soluble stain and then washed with water, which of the following describes the result that will be observed when viewing the stained slide under a microscope?

Unstained cells with no background

In the Gram-stain procedure, a clear oval in the center of a cell could indicate __________.

the presence of an endospore

You are viewing a sputum smear that has been stained with an acid-fast stain. On this smear you see 5-micrometer-long red cells. You can conclude that __________.

there are acid-fast bacteria in the specimen

In a negative staining procedure, the bacterial cells would appear __________ when viewed under a microscope.

unstained in a colored background

Acid-fast Mycobacteria differ from non-acid-fast bacteria by the presence of __________.

waxy material in their cell walls

When stained, bacteria in the genus Mycobacterium are __________.

acid fast

The acid-fast stain differs from the Gram stain procedure in the decolorizing agent used. What is the reagent used in an acid-fast stain, and why is it necessary?

Acid-alcohol is used to remove the primary stain from bacteria that do not have waxy cell walls.

Before cells are stained, the specimen must be fixed. Fixing a specimen accomplishes all of the following EXCEPT which one?

Fixation differentiates the various cells being observed

__________ are too small to be seen with the light microscope without adding a mordant and carbolfuchsin.

Flagella

__________ is important in medical microbiology because the results help physicians select appropriate antibiotics for treatment.

Gram staining

A student completes a Gram stain on a bacterial smear that has a mix of gram-negative and gram-positive organisms. The student stops the procedure without adding safranin. What would be the outcome of the Gram stain?

The gram-positive organisms would appear purple, and the gram-negative organisms would be colorless.

In the capsule stain using India ink, capsules are distinguished as __________ surrounding cells.

clear halos

What is the correct order for the Gram stain process?

crystal violet → iodine → decolorizer → safranin

The __________ charge of a basic dye adheres to the __________ charge of bacterial cell surfaces.

positive; negative

In the Gram stain, crystal violet is the __________.

primary stain

In the Gram stain, if the decolorizing step is deleted, gram-negative cells will appear __________ at the completion of the staining procedure.

purple