Ex 4: Gram Stain


Terms in this set (...)

What is the function of the Iodine solution in the Gram stain? If it were ommitted, how would staining results be affected?
to fix the dye on the slide in order to form insoluble substance. and if it is omitted then, when flushed with water and the alcohol decolorized, the bacteria will come off.
What is the purpose of the alcohol solution in the Gram stain?
for the colors to show either purple (gram +) or gram (-) and to fix the colors.
What counterstain is used? Why is it necessary? Could Colors other than red be used?
safranin, because it helps show the gram- bacterias
If your control smear does not show gram-positive cocci and gram-negative rods, can you assume that the Gram-stain reaction of your "test" organism is correct? Why?
No. At that point, you need to determine if the problem lies in the control or the staining reagents or techniques.
On the basis of Gram-stain reaction, can you distinguish species of:
1.Staphylococcus and Streptococcus?
2.Staphylococcus and Neisseria?
3.Escherichia and Proteus?
4.Escherichia and Bacillus?
What is the size of staphylococci in micrometers? In centimeters?
0.6 micrometers or 0.00006 cm.
What is the advantage of the Gram stain over a simple stain such as methylene blue?
Gram staining highlights different bacteria types through the use of special dyes. It aids in the diagnosis of a specific organism and tells the difference between gram negative and gram positive bacteria. Simple staining is unable to highlight the exact organism.
In what kind of clinical situation would a direct smear report from the laboratory be of urgent importance?
-Cervical smear - test for cancer
-a thick blood smear for malaria disease,
viability of sperm cells from semen
What is the current theory about the mechanism of the gram stain reaction?
The gram stain is a basic differential stain used to determine if a bacterial cell is gram positive or negative. Gram positive cells have a thick peptidoglycan layer that will trap the crystal violet iodine crystals and appear purple. Gram negative cells only have a thin peptidoglycan layer that allows the crystals to diffuse out of the cell and will only be seen with the application of a counterstain, such as safranin which turns the cells pink.
describe at least two conditions in which an organism might stain gram variable.
A gram-negative cell will lose its outer membrane and the peptidoglycan layer is left exposed.
or it is best to use younger cells ( 12-24hr) because older gram positive bacteria are subject to break down of the cell wall by enzymes that are produced with age which may result in gram variable staining.