How to Identify Unknown Microorganisms
Bacteria are all around us--and all over us. It is easy to culture a bacterial sample and purify it. However, it is decidedly less easy to identify the bacteria once they are grown. Following a series of experiments, however, it is possible to identify bacteria based on their physical characteristics and their behavior.
Other People Are Reading
Things You'll Need
- Purified bacteria sample
- Gram stain chemicals (Crystal violet, Gram's iodine, ethyl alcohol, safranin)
- Microscope
- Immersion oil
- Various reagents depending on results
Instructions
-
Gram Staining
-
1
Affix the bacteria to a microscope slide. Cover with crystal violet and let sit for one minute before rinsing in purified water.
-
2
Cover the sample with Gram's Iodine and let sit for one minute before rinsing in purified water. Stream ethyl alcohol over the sample until the color disappears.
-
-
3
Cover the sample in safranin and let sit for one minute before rinsing in purified water. Place immersion oil on sample and put slide on the microscope.
-
4
Focus the microscope on the bacteria sample. You will need to use the oil immersion lens to fully visualize the bacteria. If the bacteria are purple, they are called Gram positive; if they are red, they are called Gram negative.
-
5
Consult a dichotomous key for either Gram positive or negative bacteria depending on your results.
Further Classification
-
6
Identify the shape of your organism as either rods (bacilli) or spheres (cocci). The dichotomous key will narrow down the possible genera of your bacteria.
-
7
Continue using the dichotomous key to determine which tests to perform on your bacteria. Some call for you to use selective growth media and others require you to do other tests to continue on.
-
8
Keep following down the experiments listed on the dichotomous key until you get to the bottom. Use all the experiment data you have and you will end up with one specific type of bacteria.
-
1
Tips & Warnings
Not all experiments are necessary to identify all bacteria. Follow the key closely save time from doing experiments that will not aid in you identifying your organisms.
Bacteria can obviously be pathogenic, so take care as you are culturing your samples. Also, some protocols require dangerous chemicals, so follow all lab safety procedures when identifying your bacteria.
