Chapter 4 lecture notes Flashcards
Stains are dyes made of?
Organic salts
Dyes carry ___ or ___ _____ on the molecule. The molecule binds to?
(+) or (-) charge
Certain cell structures
Dyes divided into _____ or _____ based on charge
basic or acidic
These dyes carry positive charge and bond to cell structures that carry negative charge
Basic dyes
- Commonly stain the cell
- Simple stains are these dyes which are simple to use
– Simply soak a smear and rinse off
Basic dyes
These dyes carry negative charge and are repelled by
cell structures that carry negative charge
Acidic
- Commonly stain the background
* Negative stains are these dyes
Acidic dyes
Common basic dyes include
– Methylene blue
– Crystal violet
– Safranin
– Malachite green
Uses one basic stain to stain the cell
Simple stain
- Allows for increased contrast between cell and background
- All cells stained the same color
- no differentiation between cell types
Simple stain
- Used to distinguish one bacterial group from another
* Uses a series of reagents
Differential stains
Two most common differential stains
- Gram stain
* Acid-fast stain
Most widely used procedure for staining bacteria
Gram stain
– Developed over century ago
– Dr. Hans Christian Gram
Gram stain
Bacteria separated into two major groups
Gram stain. The two groups are Gram positive (Stained purple) and Gram negative (stained pink)
The Gram stain involves four reagents
1) Primary stain- crystal violet, stains all cells
2) Mordant- Grams iodine
3) Decolorizer- usually alcohol, removes primary dye from gram negative cell
4) Counter or secondary stain- Safranin, recolors cells that lose stain through decolorization
Used to stain organisms that resist conventional staining
Acid fast stain
Used to stain members of genus Mycobacterium (High lipid (wax) concentration in cell wall prevents uptake of dye)
Acid-fast stain
- Uses heat to facilitate staining
* Once stained difficult to decolorize
Acid-fast stain
Can be used for presumptive identification in diagnosis of clinical specimens
Acid fast stain
Acid fast staining requires multiple steps
1) Primary dye- Carbol fuchsin, colors acid-fast bacteria red
2) Decolorizer- Generally acid alcohol, removes stains from non acid-fast bacteria
3) Counter stain- Methylene blue, colors non acid-fast bacteria blue
- Example of negative stain
- Only stains the background
- Allows capsule to stand out around organism
Capsule stain
- Staining enhances endospore
* Uses heat to facilitate staining
Endospore stain
- Staining increases diameter of flagella
* Makes them more visible
Flagella stain
