MICRO Lab - Bacterial Smear Preparation and Gram Staining

Neither too thick nor too thin

What is an ideal thickness of a bacterial smear?

Crystal violet

What is the primary dye used in Gram staining?

Second step after primary stain

Which step in Gram staining uses iodine as a mordant?

Increases interaction between dye and bacterial cell wall

What is the function of a mordant in Gram staining?

95% ethanol

Which decolorizing agent is used in Gram staining?

Safranin

What counterstain is used in Gram staining?

Gram-positive (purple)

What is the Gram reaction of Staphylococcus aureus?

Single or pairs

What bacterial arrangement is typical of Escherichia coli?

Rod (Bacili)

What bacterial shape does Bacillus subtilis have?

Kills bacteria and fixes them to the slide

What is the purpose of heat-fixing a bacterial smear?

True

T/F: A dirty glass slide can cause bacteria to wash off during staining.

False

T/F: In Gram staining, Gram-negative bacteria retain the crystal violet dye.

True

T/F: Overheating during heat-fixing can create artifacts.

True

T/F: Gram staining can detect the presence of peptidoglycan in bacterial cell walls.

True

T/F: Old Gram-positive cultures may appear Gram-negative.

True

T/F: Both Gram-positive and Gram-negative bacteria initially appear purple after crystal violet staining.

True

T/F: The first step in bacterial smear preparation for broth cultures is shaking the tube well.

False

T/F: Differential staining uses only one dye.

False

T/F: Gram-variable species always stain consistently as either positive or negative.

False

T/F: The counterstain in Gram staining is applied before the decolorization step.