QUESTIONS Predict the effecet on Gram-positiue and Gram negatiuve cells of the f
ID: 148825 • Letter: Q
Question
QUESTIONS Predict the effecet on Gram-positiue and Gram negatiuve cells of the following "mistakes" made wben performing a Gram stain. Consider each mistake independentlhy a. Failure to add the iodine. b. Failure to apply the decolorizer. c. Failure to apply the safranin. Coran positive will be purple, Gram-negative will be colorless d. Reversal of crystal violet and safranin stains. lwould not loe alole to read. Bdth would appear purple, because durina decolorization the saçrin will coome out of the cell, and odine wil bins to orystal violet only and hence give the first purple color. 2Both crystal violet and safranin are basic stains and may be used to do smple stains on Gram positive and Gram-negative cells. This being the case, explain hou they end up staining Grum positive and Gram negative cells differently in the Gram stain. If you saw large, eukaryotic cells in the preparation made from your gumline, they were most likely your oun epithelial cells. Are you Gram-positive or Gram-negative? (You can make a good guess about this even if you didn't see your cells.) One of your lab partners has followed the recommended procedure of numing Gram positive and Gram-negative control organisms on her Gram stain of an unknown species. Her choices of controls were Escherichia coli and Bacillus subtilis. She tries several times and each time concludes she is decolorizing too long because both controls have pink cells (one more than the other). What might you suggest she try and why? She most try the experiment with new cultures because old ultures lose the ability To retain the cystal violet.Explanation / Answer
1.a. Crystal violet will leech out of the cell wall. Iodine acts as a mordant. Therefore failure to add iodine will make the cells appear Gram negative.
b. Everthing will apear purple at the end of the staining procedure
c. Gram positive cells will appear purple, but Gram negative cells will appear colourless. Therefore Gram negative cells will not be visible.
d. All the cells will appear purple at the end of staining procedure
2. This is because of the property of the stains. Crystal violet and Iodine will cross link whereas Safranine and Iodine will not cross link. Therefore crystal violet is retained and the cells appear purple.
3. Gram negative, It is the thick pepidoglycan of the Gram positive cells, that makes them to retain crystal violet.
4. She must make sure that she is using new cultures, because old cultures lose their ability to retain crystal violet.