Preparation of Smears & Simple Staining

Direct Stain

A simple stain that stains baceria

Which bacterium is on solid medium?

Bacillus, Pseudomonas...

Chemically Fix

Cover the smear with 95% methanol for 1 minute ***denatures proteins, coagulated proteins will allow specimen to stick to slide***

Heat-Fix

Dry smear is passed through a Bunsen burner flame several times ***used to kill bacterial cells & to preserve with minimal shrinkage & damage ; also used to stick to the slide***

Bacteria can be seen without staining. Why then was Koch's recommendation for fixing & staining important for microbiology?

Fixing & staining allows bacteria to be saved, re-examined, & shared for study

In heat fixing, what would happen if too much heat was applied?

It would damage & dehydrate the cells causing distortion in shape

Of what value is a simple stain?

Its a fast observation to determine morphology & arrangement of bacteria

Do not fix until smears are completely dry. Why?

May denature the smear

Simple Stain

Use only one stain

Can dyes other than methylene blue be used for direct staining?

Yes. Crystal violet, safranin, basic fuchsin - because they're all positive charges

How would pH of a stain affect the staining of bacteria?

pH determines the bacteria's charge