Microbio Lab 1 Exam 🧫

What are the 4 reagents in the gram stain lab in order?

1) Crystal violet (primary stain)

2) Iodine (mordant)

3) Acetone-alcohol (decolorizer)

4) Safranin (counter-stain)

What is the purpose of crystal violet in the gram stain lab?

Stains the cells all purple

What is the purpose of iodine in the gram stain lab?

It binds with crystal violet to form a large complex that gets trapped in the thick peptidoglycan wall.

What is the purpose of the alcohol-acetone in the gram stain lab?

Removes crystal violet from gram cells which leaves the gram+ purple and gram- clear

What is the purpose of safranin in the gram stain lab?

Stains the gram- cells pink

What happens if you don’t add the crystal violet?

No initial staining would make the cells appear colorless at first until the safranin is added which would cause them to be a pink color.

What would happen if you didn’t add the iodine?

The crystal violet might wash out during the decolorization causing a false gram-

What happens if you don’t add the decolorizer?

All the cells would remain purple and could cause false gram+ results.

What happens if you don’t add the safranin?

The gram- cells would appear colorless

What is the mordant of the gram stain lab?

The iodine is, it fixes the crystal violet in gram+ cells

What color do endoscopes stain (active)?

Green by the malachite green stain

What color do vegetative cells stain in the endospore stain lab?

Pink by safranin

Why is steam heat used during the endospore stain lab?

The steam helps the malachite green penetrate through the tough protective walls of the endospore.

What is the function or the endospore and why would a bacterial cell make it?

The purpose of an endospore is to protect and withstand critical environments. When there is a nutrient depletion or environmental stress, the endospore will go into a dormant state and form an endospore until the environment becomes favorable again.

What is the acid-fast stain lab for?

This lab is specifically used for mycobacterium. They have a waxy coat and a lipid rich cell wall. This causes them to not stain well and needs a specialized lab to be able to break down the waxy coat and rich lipid layer.

Why is steam used to get the stain into cells in the acid-fast stain lab?

The steam heat helps the carbolfuchsin dye penetrate through the waxy, lipid rich cell wall. The heat will increase fluidity of the mycolic acid found in the cell wall that helps the carbolfuchsin bind to the cellular components.