Gram Stain

What is the molecule targeted and in what structure is it found?

Peptidoglycan of the bacterial cell wall

What is the primary stain, counterstain, and decolorizer for gram stain?

Primary: Crystal violet (positive dye)

Counter stain: Safranin (positive dye)

Decolorizer: 95 % ethanol

What is the charge of the dyes used in this lab?

Positive for both primary and counter stain

What will happen if you forget to apply Gram’s iodine?

Gram positive will appear red (gram negative

What will happen if you forget to decolorize with 95 % ethanol?

Gram negative will appear purple (gram positive) W

What will happen if you over decolorize with 95 % ethanol?

Gram positive will appear red (gram negative)

What will happen if you forget to apply safranin?

Gram negative will not stain

What color does a Gram positive bacterium appear? How does the target molecule differ in each?

Gram positive (thick peptidoglycan) = purple (stain w/ crystal violet)

What color does a Gram negative bacterium appear? How does the target molecule differ in each?

Gram negative (think peptidoglycan) = red/pink (stian with safranin)

Bacteria species:

Gram +/ -

Staphylococcus aureus

Gram positive (purple)

Bacteria species:

Gram +/ -

Streptococcus agalactiae

Gram positive (purple)

Bacteria species:

Gram +/ -

Escherichia coli

Gram negative (pink)

Bacteria species:

Gram +/ -

Kelbisiella pneumoniae

Gram negative (pink)

Bacteria species:

Gram +/ -

Bacillus cereus

Gram positive (purple)