Soil samples were used as a source of bacteria. The bacteria living in the soil are less likely to be human pathogens. Nonetheless, if you do this lab, be sure to have the students securely tape up each dish after the dish has been inoculated with the soil sample. After the bacteria have begun to grow, I do not allow the students to open the Petri dish.
These photos show the results of the lab. Dishes were incubated for just 24 hours at a temperature of 30 degrees Celsius. An amazing amount of growth will occur in just 24 hours. Descriptions of each dish are found below the photograph.
I used a hole punch to make filter paper disks. The disks were then dipped into different solutions of antiseptics and disinfectants. You can see the filter paper disk on each side of the Petri dish in the above photo. In this dish, two disinfectants were tested. The disinfectant on the right did an excellent job in inhibiting the growth of the bacteria. Notice the large zone of inhibition around the filter paper disk. This disinfectant was Palmolive Antibacterial dishwashing detergent. The disinfectant used on the left was Lysol. There is only a small zone of inhibition around the Lysol disk.
In this Petri dish two antiseptics were tested. The filter paper disk on the right had the larger zone of inhibition. This antiseptic was Bactine. The antiseptic tested on the right was Triple Antibiotic Ointment.
This was the control dish. The filter paper disks were dipped into distilled water only. Notice that there is no zone of inhibition around either disk.
I hope that you will give this lab a try. It is so much fun for students to grow bacteria. Here is the link to this lab in my store on TeachersPayTeachers.com: