Gram Stains

What is the primary stain for Gram staining?

Crystal Violet

What is the mordant for Gram staining?

Gram’s Iodine

What is the purpose of the mordant during staining?

sets the crystal violet into all cells

What is the decolorizer in Gram staining?

acetone-alcohol

How does the decolorizer affect Gram positives?

thick cell wall is dehydrated, trapping the crystal violet in place

What 2 things make up the thick cell wall of Gram positives?

1. peptidoglycan

2. teichoic acids

How does the decolorizer affect Gram negatives?

outer thin cell wall is dissolved/forms holes, allowing crystal violet to exit the organism

What does the outer thin cell wall in Gram negatives consist of?

lipopolysaccharides (LPS)

What is the counterstain in Gram staining?

safranin

Blue/Purple organisms are Gram (positive/negative).

positive

Red/Pink organisms are Gram (positive/negative).

negative

What would over-decolorizing do to your stain?

Gram positives would appear Gram negative

What would under-decolorizing do to your stain?

Gram negatives would appear Gram positive

How old should a culture be to use for staining?

18-24 hrs

Why do we not use cultures older than 24 hours?

older cultures can be easily decolorized

Cultures older than 24 hours may appear Gram (positive/negative).

Gram negative

Smears that are too thick can what affect on staining?

Gram negatives will appear Gram positive

How would you report this stain?

GPC

How would you report this stain?

GPR

How would you report this stain?

GPR w/ spores

How would you report this stain?

GPR w/ spores

How would you report this stain?

GNC

How would you report this stain?

GNR

How would you report this stain?

yeast

How would you report this stain?

yeast

Nonbacterial cells and cellular debris should appear Gram (positive/negative).

Gram negative