Labs 6-11 Flashcards
Why is it important to prepare thin smears
The thickness of the smear will determine if you can visualize individual cells, their arrangement, or details regarding microstructures associated with cells
Name several goals in preparing a smear
To cause the cells to adhere, to insure that shrinkage of cells does not occur, to prepare thin smears
Why is it important to be sure to cool the loop completely before inserting it into a medium
A loop that is too hot Will spatter the medium and move bacteria into the air
Describe the procedure for making a bacterial smear using a liquid media
To loopfuls of liquid containing organisms are placed on the slide; the smear is allowed to dry at room temperature; slide is passed through flame several times to heat-kill and fix organisms to the slide
What is the first step in the procedure for making a bacterial smear using a solid media
To loopfuls of sterile distilled water are placed on the slide
Name three of the most commonly used dyes for simple staining
Methylene blue, basic fuchsin, and crystal violet
Why do dyes work well on bacteria
Because they have color bearing ions that are positively charged
What is another word for color bearing ions
Chromophores
What three physical characteristics can be determined by simple staining
Morphology, size and arrangement
Negative stains are _____ and thus have a ____ charged chromophore
Negative stains are acidic and thus have a negatively charged chromophore
Two examples of a negative stains
India ink and nigrosin
Negative staining can be useful for studying what and why
Cell dimensions because heat fixation is not performed no shrinkage of cells occurs and size determinations are more accurate
Three examples of when negative staining is more useful
Size determination, capsule observation, observing spirochetes
Which cell has a thicker PG layer
Gram-positive
Which cell has an outer membrane
Gram-negative
What is the primary stain in gram staining and color results
Crystal violet; both cells stain purple
What is the mordant in gram staining and color results
Grams iodine; both cells stain purple
What counterstain is used in gram staining and color results
Safranin; +=purple, -=pink
What is used for decolorization in gram staining and color results
Ethyl alcohol; +=purple, -= “clear”
Final color results of gram staining
Gram-positive will be purple, gram-negative will be pink
What significant difference in structure determines whether the dye-mordant complex is removed from the Gram-negative cell or remains associated with the gram-positive cell
Thickness of the PG layer that comprises the cell wall as well as the presence of an outer membrane
Can gram-negative bacteria ever convert to Gram-positive bacteria
No
Why is it important to prepare thin smears
Thin smears allow the observation of individual cells and any arrangement in which the cells occur; thickness also affects the colorization
What is the most critical step in the Gram stain procedure
Decolorization
