Staining Specimens

What is the most common stains we use?

• Gram stain

• Ziehl-Neelsen (acid-fast) stain

T/F You can over decolorize your stain if you leave it on too long or are too aggressive with it EVEN if you applied the other stains

true

What stains do we typically used for yeast?

Crystal violet and methylene blue

What stain confirms the identity of fungal organisms?

Lactophenol cotton blue

Why are gram stains used?

to categorize bacteria

• Gram-positive or gram-negative

How do we know if bacteria is gram + or gram - ?

based on the cell wall structure

What are the 4 steps required with gram staining?

Primary stain, a mordant, a decolorizer, and a

counterstain

What does the mordant stain do when doing a gram staining?

fixes dyes to the structures (cell wall)

What is the primary stain for gram staining?

crystal violet

What is the mordant stain we use for gram staining?

Gram’s iodine solution

What is the decolorizer stain we use for gram staining?

95% ethanol or acetone

What is the counter stain we use for gram staining?

basic fuchsin or safranin

T/F We heat up the gram stain until it is hot.

False - warm, not hot - do NOT overheat

What does gram positive bacteria look like?

purple blue in color and retain the crystal violet solution

What does gram negative bacteria look like?

reddish, pink and retain the safranin counter stain.

What does the KOH test determine?

Determines the true Gram status