Names of Partners______Date ______
Thinking like Bacteria
Most of us do not realize how many times a day we encounter microbes. Nor do we realize where we come in contact with them. The very air we breathe is laden with bacterial and fungal spores that we inhale day in and day out. In this lab, we will take samples from different areas of the school and see what grows and which areas have the highest microbial load.
What do you feel are the best condition for the growth of bacteria and fungus? (Look it up)
Which area would you like to investigate and why do you think this area would have the highest number of microbes in it?
Materials:
· 2 Sterile Petri dishes
· 2 Sterile swabs
· Marker
· Sterile water
· Tape
· Colony Counter (2nd day)
· Autoclave (2nd day)
First day Procedures:
1. In groups of two, select an area you would like to test and put this location up on the board so that your classmates know which areas are being test
2. Each group of two should get two sterile, plastic Petri dish containing growth medium called agar. DO NOT OPEN THE PETRI DISHES UNLESS INSTRUCTED TO DO SO AND USING THE PRECAUTIONS GIVEN TO YOU BY YOUR TEACHER??
3. There are two parts to the Petri dish, a larger top and a smaller but higher bottom. Turn your dish over so that the bottom part of the dish is facing up. Using a marker, write your names and the location being tested on the bottom, sides of the dish.
4. Obtain a package of sterile cotton swabs. You will open the package from the stick side, leaving the cotton swab part still in the sterile packaging. Do not do this until you are ready to swab.
5. When you have gotten to your location, remove the swab by grabbing onto the stick, immerse the swab into the sterile water (recap immediately), and swab the area being tested, turning the swab around to get the maximum possible sample. One turn of the swab should do the trick.
6. Open the Petri dish up only a crack (like a clam) and gently swab the area on the top of the agar as instructed by your teach. Do not press down or you will dig into the agar. You should apply the cotton swab in a zig-zag pattern, trying to cover the entire surface of the agar. Do this to both of the plates given to you. Immediately after inoculating the plate, close the dish up.
7. After inoculating the plate, put the used swab into the wrapper it came out of and bring it back to the classroom to be autoclaved (sterilized). Once back in the classroom, tape the Petri dish closed with two pieces of tape on either end of the plate.
8. Store your dishes upside down, agar side up (to avoid condensation collecting on top of your specimens) in a designated location.
9. Incubate at room temperature for 24 to 48 hours at room & body temperature (22`C and 37`C)).
10. Using a Clorox wipe, wipe down your work area thoroughly.
Second Day Procedures:
11. After the incubation period, retrieve your Petri dish but remember not to open the dish!!
12. Place your dish on a colony counter or your lab table, and count the number of colonies (dots). If the number is too large to count, select a section; count them and then multiple by the fraction you divided the dish into.
13. Also note the different types of microbes you have growing. Count up the number of varieties. This is done by seeing how many different looking types of colonies you have.
14. Record the number of colonies and varieties on the data table below and then share this with the class.
15. Place your soiled Petri dishes in the autoclavable container to be sterilized.
16. Using a Clorox wipe, wipe down your work area thoroughly.
Data Table: Areas Swabbed versus amount of Growth
Partners / Area Tested / # of Colonies / # of VarietiesAnalysis:
1. Which area tested had the greatest number of microbes? Why do you think it had the greatest amount?
2. Which are had the least number of microbes? Why do you think this was so?
3. Why were the dirty swabs and the used Petri dishes discarded in the autoclavable vessel instead of just
throwing them into the classroom garbage pail?
4. Why did you never open up the Petri dishes in the classroom handled them with strict sterile
procedures?
5. What was the very last thing you did on both days and why did you do this?