Bacteria
Feed Them and They Will Come
Outside of laboratory time:
1)Read the article on “Good Germs and Bad Germs”. You will need to carry this information with you the rest of your life so maybe you should buy the book mentioned in the article.
2)Read your text regarding bacteria taxonomy. How many Kingdoms are we investigating? Are bacteria in our domain?
3)Look in your text for names of general bacterial “types” (by shape) or lug the giant thing (your text) to lab.
In the Laboratory:
1)Review aseptic techniques:
a)Remember that the purposes of aseptic techniques are to prevent the cultures you are using from being contaminated (recall the propagule lab and remind yourself that we are studying the masters of propagulity) and to keep your study organisms from escaping and contaminating the environment.
b)Wipe the surfaces of your work area with disinfectant before and after you work.
c)Wash your hands before and after you work.
d)Don't put your swabs on the table, put them immediately into the disposal container.
2) Now refresh your microscope technique. If you did not learn the routine in high school or in a previous class, tell your lab instructor so they can “Check you out”. Remember: Always start on low power, locate and focus on the specimen, carefully switch to high power and always focus away from the object.
3) Obtain a “bacterial types” slide from the tray in the patch where the materials have been prepped. Draw the three types in your lab manual and label each (use 400x).
The slides are laid out as shown here--
Name the three types using any adjective that relates to their general appearance. Alternative one A-2 A-3 A-4
Name for Type one ______
Name for Type two ______
Name for Type three _____
Obtain at least four alternatives for each name by comparing your choices with your peers.
The class consensus names are:
(you will need to compare these to the “standards” given in your text)
How much of each “field of view” is occupied by an individual cell? Does your estimate agree with your patch-mates? How big is an individual bacterium? Have we looked at anything else this small? Draw an individual bacterial cell to scale and next to it draw the next smallest organism we have studied so far.
4)Now you are ready to prepare a lawn of potential bacteria. You each need to prepare a plate. You can get together in groups to make comparisons and ask interesting questions.
a)Obtain a plate (prepared and in the metal bins in front) and cotton swab.
b)Decide where you will obtain your potential bacteria. Remember, they are everywhere.
c)Take your plate and swab to where-ever you decide to sample.
d)Twirl the swab on your area of choice and then prepare your lawn as follows:
--Take the lid off the plate.
--Apply the swab you twirled on an area in a zig-zag motion over the entire surface as shown below (a).
--Rotate the plate 90 degrees and repeat the zig-zag (b below).
--Dispose of the cotton swab in the container provided.
5)Choose one to three of the potential antiseptics from the selection in the front of the lab.
6)Formulate a hypothesis concerning the effectiveness of your choices. Record it in your lab notebook
7)Apply the antiseptic by
a)pouring the antiseptic into a shallow dish
b)using a pair of forceps, submerge a paper disk in each solution and while it soaks
c)mark the underside of your agar plate with a wax pencil designating where you will place the disk (apply the disinfectant)
d)place the paper disk on the agar plate (on a zig-zag) over your marked spot and leave it for 2 minutes
e)remove the disks and toss them
f)recover your agar plate, mark it on the lid and place it in the film canister for incubation.
8)Concentrate on feeding the whole spectrum of bacteria. What does TSA stand for? Why is that a standard medium? What else might bring out some of the shyer bacteria? Do we have any alternative foods for bacteria? Set up a plate that will address the hypothesis: Many functional groups co-exist on common surfaces and become visible when they grow in sufficient numbers to show up on a plate.
Next week
Fill in the following table, which by next week will be in your lab notebook:
Test Substance Diameter of the Zone of Inhibition (in mm)