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Saturday, October 16, 2004

Staining

DEFINITIONS:

Staining - refers to simply coloring a specimen with a colored dye.

Simple Stains - using a simple basic dye, such as crystal violet, in order to view the shape , size, and arrangement of cells. The simple stains include: differential, Gram, acid-fast, and endospore stains
Multiple and Differential Stains - The most popular stain used in microscopy. These stains involve multiple dyes in order to distinguish cells under the microscope.
Gram Stain - Named after Hans Christian Gram, differenciates between Gram-positive purple and Gram-negative pink stains and is used to identify certain pathogens.
[Visit this page to watch the Gram-stain procedure.]
Special Stains - These are stains that include the acid-fast, endospore, capsule and flagellar stains.
Acid-Fast Stain - is used for staining cells of the genera Mycobacterium and Nocardia. These cells have a waxy material that repel the water-based dyes of the Gram Stain. The Mycobacterium and Nocardia cause many human diseases, such as TB, leprocy, and other pulmonary and skin infections.
[scroll halfway down this page and watch the acid-fast stain procedure.]
Endospore Stain - The cell walls of endospores are impermeable to most chemicals, and being in the genera Bacillus and Clostridium, cause diseases such as anthrax, teatanus and gangrene.
The staining process involves both a primary stain and a counterstain.
Capsule Stain - a stain used to reveal negatively charged bacterial capsules. The encapsulated cells will have a halo appearance under the microscope.
Flagellar Stain - Flagella are usually invisible under light microscopy, but their identification and anatomy are important in determining some pathogens. Certain chemicals that bind to the flagella are used in the staining process. The flagella color may change or an increase in contrast should make them visible.
Agar - a gel-like polysaccharide isolated from red algae and used as a thickening agent.
MEDIA TYPES:
Defined - is used when exact chemical composition is known. Pure chemicals are in the mixture and need a buffer added to them. These types are good for looking at nutritional requirements or growth factors.
Selective - contains substances that either favor the growth of some organisms or inhibit the growth of unwanted ones. This helps to narrow down the microorganism of interest. (Glucose salts)
Differential - created in mind that different organisms metabolize different materials in different ways. A bacteria type can change a substance in a recognizable way. (Blood agar used for strep testing)
Complex - these agars contain a variety of ingredients.
COLONIES:
A bacterial colony
A fungal colony


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3 Comments:

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