Bacteria: Here, there and everywhere…
An Inquiry Investigation
Introduction:
Bacteria - They're everywhere! Bacteria are the huddled masses of the microbial world, performing tasks that include everything from causing disease to fixing nitrogen in the soil. The estimated number of bacteria on Earth is five million trillion trillion -- that's a five with 30 zeroes after it. When people think of bacteria, they likely first consider the nasty ones that cause disease, but the bacteria inside all animals combined -- including humans -- makes up less than one percent of the total amount. By far the greatest numbers are in the subsurface, soil and oceans.
Finding bacteria in any given environment should not be a problem, but you need to be familiar with a microbiologist's tools of the trade. Agar, a nutrient broth that serves as a food source for the bacteria, has been prepared for you in a machine called an
autoclave and poured into a sterile petri dish. The autoclave heats the liquid agar to a high temperature and pressure, which sterilizes it. The hot liquid is poured into a sterile petri dish, covered with a lid, and it cools to a gelatin-like consistency. From this process, some condensation can build up on the lid: be careful not to allow this liquid to drop onto your agar surface. This way you are beginning with a bacteria-free surface on which to culture the bacteria you collect.
You will be using cotton swabs to obtain bacteria from a variety of surfaces either from around home or around ZEHS. Once your petri dish has been inoculated with bacteria, it will be sealed with tape and placed into an environmental chamber. The chamber provides a constant warm temperature and light; lovely conditions for bacterial growth
Objectives:
1. To observe bacterial growth and make observations of that growth over several days
2. To determine which substances have the most effect on inhibiting bacterial growth (the best “antibiotics”)
THE INVESTIGATION PLAN
Getting Started:
1. You and your partner(s) will look over the following given information regarding procedure, and observation.
2. Discuss as a group what areas you would like to swab for bacteria as well as different treatment options for those areas. If you have
something at home that you would like to bring in as a treatment option (ex: essential oils, certain cleaning products, etc…) now is the time to plan to bring that in.
The Experimental Procedure :
Collecting Bacteria
A.Materials that will be provided to your group:
** If you need other things, then bring them in
3 Petri dishes with sterilized nutrient agar, cotton swabs, 1 permanent marker, clipboard, tape, environmental chamber, several treatment options (see board)
B. The Procedure DAY 1
1. You and your partner(s) will choose three sample locations around the school (or home if you plan ahead). You may not enter the cafeteria food area (per health department codes) and I do not recommend the toilets in the bathroom – they get cleaned regularly and you will not get very good results. Try to think of places that will yield good bacterial growth
2. Carefully, and quickly, turn each petri dish upside down so that the gel side is up and any condensation on the lid stays down – do not open the lid. You will need to keep your plates in this direction so the water doesn’t drip onto the agar. Using your marker, mark off 4 even sections on the underside of each dish (draw them if they are not already lined in the dish) and label the edges of each plate as shown in the picture below:
Once all of your plates are prepared, you are ready to go out and collect samples… NOTE: If you are swabbing a dry surface, be sure to wet the Q-tip end in water before swabbing -wet it in the drinking fountain, not your mouth!
3. COLLECTION: Hold a sterile Q-tip in the middle, being very careful not to touch the tips that will collect your samples. Go to your first area and quickly swab using one end of the Q-tip. Carefully open your 1st dish just enough to
of the Q-tip in the sections marked 1ta, 1tb, and 1tc. Work quickly and carefully while inoculating your dish as to avoid any extra contamination.
4. Repeat this procedure at the other TWO locations you have chosen – KEEP YOUR PETRI DISH COVERED AND CLOSED AS MUCH AS POSSIBLE!
5. Return to the lab:
Carefully place your petri dishes on your lab table area. Try to make logical treatment predictions based on the areas you have chosen. For example, if you have swabbed your eye then the treatment options could be water soap
(because hopefully you recognize that you should never put bleach or alcohol in your eyes
In the “treatment” sections (1ta, 1tb, 1tc, 2ta, etc…) of your dishes, you need to place 1 drop of a chosen treatment solution. Place the 1 drop and leave it alone, do not try to spread it out – this will happen on its own. You will choose 3 different treatments for each area swabbed (ex: 1ta, 1 tb, and 1tc). The
treatment choices available from me are as follows:
1. Bleach solution 5. Germ-X sanitizer solution
2. Isopropyl Alcohol 6. Windex Multi-Surface Disinfectant 3. Anti-bacterial Soap solution 7. Vinegar
4. Water 8. Mouthwash
9. Other? Did you bring something in?
6. Once all plates have been swabbed and treated as directed, place a strip of masking tape along the outside edges of your dishes to seal them closed and put your name(s) and hour on the tape so you can find your dishes again. Place your petri dishes upside down (lid-side down, to prevent condensation drop) in the class box/tray. This will be put into an environmental chamber and will be examined again over the next few days.
DAYS 2, 3, and 4
7. OBSERVATION: Recheck each of your plates after 1 day, 2 days, and 3 days.
Count and record the number of bacterial colonies on each section in your data table. Note: If there are too many to count individually or if the plate
is completely covered with bacteria, record "lawn" in your data table. Also give a description of the growth on each section – include details such as color, shape and size of the colonies. Take pictures of your dishes on each day of observation. These need to be included in your observations and data.
*** Ignore "fuzzy" appearing colonies that are actually fungi, or the large white
Example of Bacterial Colonies on Plate
8. 9.
