Gram Staining

Streak Plate

A technique used to isolate individual bacterial colonies from a mixed sample.

Nutrient Agar

The most common medium used to grow bacteria for a streak plate.

Gram Staining 4 Main Steps

1. Crystal violet (primary stain), 2. Iodine (mordant), 3. Ethanol (decolorizer), 4. Safranin (counterstain).

Primary Stain

The first stain used in Gram staining, which is Crystal violet.

Counterstain

The dye used as a second stain in Gram staining, which is Safranin.

Function of Iodine in Gram Staining

A mordant that binds with crystal violet to make the dye stay better

Ethanol in Gram Staining

The decolorizer that removes the crystal violet-iodine complex from Gram-negative cells.

Bunsen Burner

A device used to create an updraft to keep airborne contaminants away and sterilize tools during Gram staining.

Clam-Shell Technique

A method of slightly opening the lid of a petri dish to minimize exposure to airborne contaminants.

Gram-Positive Cells

Bacteria with a thick peptidoglycan cell wall that stain purple and are generally treatable with antibiotics.

Gram-Negative Cells

Bacteria with a thin peptidoglycan cell wall and an outer lipopolysaccharide layer that stain pink and are more difficult to treat with antibiotics.