Lab Report Week 4- Gram Staining

Introduction: Gram staining is a method of staining used to differentiate bacterial species into

two large groups, gram-positive and gram-negative. Gram staining differentiates bacterial

species by the chemical and physical properties of their cell walls by detecting peptidoglycan,

which is present in the cell wall of gram-positive bacteria. Gram-positive retain the crystal violet

dye while gram-negative does not. Gram positive will appear purple and gram-negative will

appear pink after a counterstain such as safranin is added.

Purpose: To properly perform staining procedures which is used to classify bacteria into two

groups.

Materials and Methods: Glass slides, sheets of bibulous paper, tap water, crystal violet stain,

iodine-potassium iodide, beaker of alcohol, safranin stain, mountant, slide cover slips, and high

powered microscope.

Results and Discussion: During this lab, students had to perform a Gram stain on prepared

bacterial slides then observe the results of the Gram stain.

Staining Procedures:

1. Obtain a slide and a sheet of bibulous paper. The bacterial smear appears a s a

white spot on the same side of the slide as the identifying mark (X).

2. Completely cove the smear with several drops of crystal violet for one minute.

3. After one minute, run tap water over the slide to remove the excess crystal violet.

Mordant Procedures:

1. After staining, completely cover the bacterial smear with several drops of iodinepotassium iodide for one minute.

2. After one minute, run tap water over the slide to remove the excess iodine-potassium

iodide.

3. Blot the excess water from the slide by laying the slide on the bibulous paper and

pressing gently. Do this for both sides. (Do not rub the slide against the paper or the

bacterial smear will wipe off.)

Decolorizing Procedures:

1. Immerse the slide in the beaker of alcohol and stir for 30 seconds. (Be sure the

smear is covered with alcohol.) The alcohol will dissolve away some or all of the

statin.

Counterstaining Procedures:

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