Disinfectant Lab

I. Question: Which disinfectant will destroy bacteria best.

II. Purpose: To find out which disinfectant will work best against two types of bacteria – E. coli and B. cereus.

III. Hypothesis: I think that, since Betco and the school cleaner are not meant for to be used in cuts and wounds, and the others are, these two will be more powerful.

IV. Procedures:

A. Written Procedures:

1. Decide at your table which subgroup will use E. coli and which will use B. cereus and subject these pure cultures to different disinfectants.

2. Label your dish.

3. Record the names of the disinfectants and their color on you data chart.

4. Using the sterile swab, wipe some of the bacteria from the pure colony, and then wipe the swab again on your new sterile petri dish.

5. You will need to collect the different disinfectants and water onto your petri dish by doing the following:

a. Dip the coloured circle in the antiseptic you choose, letting the paper absorb the liquid.

b. Remove the excess substance from the disk by gently tapping it onto the side of the container. If the disk is dripping when placed into the dish, the excess water will blow to the next disk and mix, thus ruining your experiment.

c. Place the disk gently into the dish, near the side. Close the lid after each disk is added to minimize the amount of outside bacteria floating in.

6. Incubate the dishes for two twenty-four hour periods.

7. Observe, draw, and label the results for both species.

8. Measure the zone of inhibition and record on the data table

9. On the last day, rank the antiseptics from best to worst.

10. To write the results for both species, you bill need to share with the other subgroups at your table.

11. Answer the remaining questions on the data sheet.

B. Materials List:

· Sterile petri dish and agar

· Pure colony of both species.

· Sterile swab

· Coloured paper disks

· At least six kinds of disinfectants

· Sterile water

· Tweezers

· Data sheet

· Incubator

V. Observations/Data:

A. Day one: The Betco did the best on the B. cereus, with a whopping 9 mm. The E. coli exhibited no growth.

B. Day two: The Betco is still leader in the B. cereus; other disinfectants’ effects have greatly diminished. The E. coli has grown, and the Betco is also leader there.

I. Conclusion and Analysis: The data I collected supported my hypothesis: in each of the species, Betco worked the best. However, the school cleaner did not have any effect. This fact is terrifying, because that is the stuff the janitor uses to clean the classrooms with.

II. New Questions: Do these disinfectants work similarly on fungi? Are some bacteria more resistant to these disinfectants than other?