Sponge Soup Lab

Background Antibiotic or disinfectant discs are often used to determine if a particular bacterium is susceptible to a type of antibiotic or disinfectant. If the antibiotic or disinfectant works successfully, a clear ring (an area where bacterial growth is inhibited) will appear around the disc in 24-48 hours. The ring is called the zone of inhibition. Depending on how well the disinfectant works, you will see more or less area around the disc that will be free of bacterial growth.

Pre-Lab Questions: 1. What are the best conditions for bacteria growth? 2. What are some methods that bacterial growth can be controlled? 3. Define the lawn of bacteria. 4. Define zone of inhibition. 5. What is the relationship between the size of the zone of inhibition and the effectiveness of the disinfectant?

Problem: A food poisoning outbreak has swept through the town of Newtown over the holiday break. A link has been found between infected families and the Gobble brand turkey purchased and consumed by each family. There were two differences between the households that became ill and those that did not. Scientist noted that the type of cleaning methods/agents used to clean the kitchen were different, as well as whether or not rags/sponges were used to wash the dishes. Sponges from the infected households were collected. Your assignment is to determine which disinfectants work best in controlling the growth of bacteria.

Materials: Rubber gloves Safety goggles Petri dishes Ruler Sharpie Nutrient agar Sponge Inoculating loop Paper discs Sterile water Antibacterial disinfectants Masking tape Incubator

Data Table 1.1 Type of Disinfectant Use Zone Name of Disinfectant 1 Sterile H2o (Control) 2 3 4 5 6 7 8

Diagrams 1.1 Zones of Inhibition 2 3 4 4 Plate 1 Plate 2

Size of Zone of Inhibition (mm) Data Table 1.2 Size of Zones of Inhibition Zone Name of Disinfectant Size of Zone of Inhibition (mm) 1 Sterile H2o (Control) 2 3 4 5 6 7 8