Gram Flashcards
What is the
Classification
target tissue
staining principle
mechanism of staining
positive controls
for Gram stain
Classification - microorganism stain
target tissue gram + and gram - orgs
staining principle- differential staining
mechanism of staining
-ionic bonding
positive controls- appendix, tissue with known orgs
What is the cell wall of gram pos and neg orgs
Gram pos- peptidoglycan
gram neg- LPS
primary stain
positively charged
-crystal violet and Gentianl biolet
goes through the cell wall to form ionic bonds with negatively charge phosphate groups in nucleic acid
both types should be stained purple
2nd iodine
goes into the cells with a combining with crystal violet = large complex
trapping agent
3- decolorization
alcohol or acetone
-concentration is important
-50-70% decolorizes the cell quicker than higher concentrations
-drain all water from the slide PRIOR to decolorization
-timing is critical
What happens in decolorization
-peptidoglycan gets dehydrated leading to pore reduction in Gram Pos bacteria
-lipid is extracted and this causes larger pores in the wall of Gram neg bacteria
what are the effects of decolorization
gram neg bacteria = colorless
gram pos= purple
4th counterstain
safranin, neutral red,
-forms ionic bonds with free sites on nucleic acid of gram neg
-bacteria that is old or damaged because of age or chemicals will look gram neg
what happens when you decolorize
too long
too short
too long- all orgs look red
too short - differentiation may not happen so all bacteria will look blue
What happens when you counterstain
too much
not enough
too much
-leaches CVI complex from gram pos and will stain with counterstain = false gram neg
too little - fail to stain gram neg
What is a modification you can make to stain collagen and cytoplasm a different color
add an acid dye to counterstain
