Transcript To kill anything that is on the loop…so you do not contaminate your

Purpose: Use procedure to identify if bacteria is gram positive or gram
negative. This would help someone know how to treat an infection.
Prelab:
1. Why do you run the loop in the fire?
To kill anything that is on the loop…so you do not contaminate your experiment.
2. Why do you have to wait for the water to evaporate before heatfixing?
If you don’t and you “fix it”, the water will boil and the bacteria will boil away
with the water leaving you with no bacteria.
3. Fixation:
Waving the slide through a flame several times
The purpose is to make the bacterial cells stick to the slide
4. Primary Stain:
Called “crystal violet”
Stains bacteria purple
Gram + will soak this in
5. Mordant:
Called “iodine”
Forms a complex with the crystal violet in gram + bacteria, making it
harder to wash off throughout the remainder of the procedure
6. Ethanol:
Does nothing to gram + bacteria
Washes stain off of gram - bacteria
8. Counter Stain:
Called “safranin”
Stains gram – bacteria red
9-10. What color is the bacteria?
Gram Positive is Purple
Gram Negative is Red
11. What is a “Smear”
Bacteria rubbed into a drop of water
 The smaller the drop of water you use for your smear, the faster it
will evaporate.
 You DO NOT NEED a big “chunk” of bacteria…this will be too much
to see.
 Do not rush the evaporation process. Be PATIENT!
 Read the directions and follow them!
 If it says, “drop” then only use a drop. If it says, “apply” then
cover the slide (squirt).
o Record which tube you took your bacteria from and record the
number in the appropriate space.
o Record whether or not it is gram + or gram o Draw what you see in your slide
o Record the shape and arrangement by using the Latin terms in
your notes
o Write the genus name of the bacteria based on the above.