Lab Report 16: Control of Microbial Populations—Effect of Chemicals

Lab Report 16: Control of Microbial Populations: Effect of Chemicals1. What was the purpose of this lab exercise?2. Complete the following table with your observations:Disinfectant / Antiseptic | Name of the bacterium | Zone of inhibition | Comments3. Name the chemical that inhibited both bacteria tested.Bacterial Cultures- Escherichia coli broth culture- Staphylococcus aureus broth cultureMaterials- Nutrient agar- Sterile petri plates- Forceps- Filter paper discs- Bunsen burner- Sterile cotton swab- Wax pencilSuggested Disinfectants / Antiseptics- Hydrogen peroxide- Rubbing alcohol- Lab disinfectant- Copper sulfate (1%)- Any home disinfectant/antiseptic productProcedure1. Boil water in a beaker and place four tubes of nutrient agar in it.2. When the medium is completely melted, transfer the tubes to a test tube rack and let them cool slightly.3. Before the medium solidifies, pour two tubes of agar into each sterile petri dish, swirling gently to obtain an even distribution. Allow the agar to solidify.4. With a wax pencil, label the bottom of two petri dishes with the name of each bacterium. Divide the petri dishes into four quadrants and label each with the name of the chemical agent.5. Disperse the bacterial cultures by rolling the tubes between the palms.6. Dip a sterile cotton swab into the culture and press it against the inner wall of the culture tube to remove excess liquid.7. Partially open the petri dishes and inoculate the entire surface of agar with the inoculum.8. Repeat steps 6 and 7 at least two more times to ensure full coverage of the surface area and even distribution of the bacteria.9. Using a pair of sterile forceps, pick a filter paper disc and touch it (do not dip to avoid excess chemical that may run on the agar surface) to one of the disinfectants or an antiseptic solution.10. When the chemical is soaked into the disc, place the disc in the center of the matching, labeled quadrant of the culture dish.11. Tap the disc gently against the agar so that it does not fall off when the plate is inverted during incubation.12. Repeat steps 9, 10, and 11 for other chemicals and for both agar plates.13. Incubate both agar plates at 37°C for 24 hours.14. Check for the presence/absence of a zone of inhibition around each disc.15. Complete the lab report.