(7) Flashcards
staining procedure that allows distinction between cell types or parts of cells; often involves more than one stain, but not necessarily. Allows a microbiologist to detect differences between organisms or differences between parts of the same organism.
differential stains
organisms that have other important cellular attributes, such as a capsule, spores or a flagella
structural stains
a step that a occurs between the application of two basic stains; the decolorization step is what makes the Gram stain differential
decolorization
the first stain applied in many differential staining techniques; usually subjected to a decolorization step that forms the basis for the differential stain.
primary stain
a chemical that fixes a dye in or on cells by forming an insoluble compound thereby promoting retention of that dye; enhances staining; Iodine is added to enhance crystal violet staining
mordant
iodine is added as a mordant to enhance crystal violet staining by forming a _____ _______ _______ __________
crystal violet-iodine complex
stain applied after decolorization to provide contrast between cells that were decolorized and those that weren’t; safranin
counterstain
What is the important of a differential stain?
It allows a microbiologist to detect differences between organisms or differences between parts of the same organism. They do not only allow determination of cell size, morphology, and arrangement (as with simple stains) but information about other features as well.
How many basic stains are used in the gram staining procedure?
Primary stain (crystal violet) & counterstain (safranin)
What color are Gram positive cells after the gram staining procedure? Gram negative?
Gram positive cells- purple
Gram negative cells- reddish-pink
How can over-decolorizing or under-decolorizing affect the gram staining results?
It is possible to over-decolorize by leaving the alcohol on too long and get reddish Gram-positive cells.
It is also possible to under-decolorize and produce purple Gram negative cells.
What is tested for using the KOH procedure?
Secondary test for Gram identification
What is the mechanism of action of this test?
The KOH dissolves the cell walls of Gram negative bacteria, but does NOT affect Gram positive cells.
What is considered a “positive” KOH test? What does this indicate?
Gram positive cells are not lysed, no free DNA, no viscosity will be observed.
What is considered a “negative” KOH test? What does this indicate?
The Gram negative bacteria will lyse and cellular contents, including DNA, spill out of the cell. They will look like boogers and will stick to a loop when touched.
