Mouthwash Vs Bacterial Growth Lab

Assessment of Mouthwash Brand vs. Bacterial Rate of Growth CA Standard 10d: Students know there are important differences between bacteria and viruses with respect to their requirements for growth and replication, the body’s primary defense against bacterial and viral infections, and effective treatment of these infections.

Research Question: Do different brands of mouthwash have the same level of antibacterial effectiveness? Background: In your lab report, discuss bacteria, their growth requirements, and the importance of mouthwash for dental hygiene. Hypothesis: You write this! Remember the format: If…then…because Variables: Independent (IDV): Mouthwash brands Dependent (DV): Zone of inhibition Materials: • Bleach solution, 10% (for disposal) • Marking pens • Mouthwash • Sterile paper disks, 4 per dish • Isopropyl alcohol • Petri dishes filled with nutrient agar • Bacterial stock cultures • Sterile Inoculation Loop • Forceps • Ruler and transparent tape Safety Precautions: After use the agar plates will contain viable microbes. Do NOT OPEN the plates. Be sure to sterilize your work area before and after working on the lab with the bleach solution, and wash your hands carefully with soap before leaving the lab. Be careful with the bleach solution it may irritate or burn your hands. Procedures: 1. Draw quadrants on the bottom of the nutrient agar-filled Petri dish using a marking pen. 2. Using a sterile inoculation loop, touch the bacterial stock culture. 3. Streak the entire agar plate and wait a few minutes for the plate to dry using the following technique. REMEMBER: Do not dig in with the inoculation loop! It is enough to gently move the loop across the surface. With colony on loop from starter plate, begin in the middle and move in small circles outward toward the edges of the plate. It is your goal to get an even distribution and cover as much of the surface as possible. 4. Soak three different paper disks each in a different mouthwash solution. Soak a fourth disk in the control which is deionized water. 5. Using forceps, shake off excessive liquid and place one paper disk in a quadrant. Press down lightly with forceps to set the disk in place. 6. Sterilize the forceps using isopropyl alcohol between placing samples on the agar plates. This will prevent cross contamination. 7. Label the bottom of the plate along the plate edges. Do not write under the disk-this area needs to remain clear in order to measure the zone of inhibition. 8. Repeat steps 5-8 using the three remaining disks. Data table, Graph, and Results 1. Using the class data, construct a data table for the different mouthwash solutions and the zone of inhibition for each solution. You will be measuring diameter in millimeters each day for three days. 2. Calculate the mean zone of inhibition for each solution, and put this value in the table as well. 3. After the third day you will create a graph of each mouthwash solution and its mean zone of inhibition. Since you are comparing the mean values what type of graph will this be?

Conclusions: 1. Write a paragraph with the following:  Restate the research question and your hypothesis in the paragraph.  What do you conclude from the data? Was one mouthwash more effective than another? Does your data SUPPORT or REJECT your hypothesis?  Do not forget to include your error analysis (what were some errors that could have been made in doing the lab) and suggestions to improve the lab. Teacher Notes

 This lab was adapted from Flinn Scientific Inc. Publication No. 10598. It is titled: Assessment of Over- the-Counter Antibacterial Products.  Concepts addressed in this lab are: o Antibacterial agents o Bacterial inoculation o Zones of inhibition  Materials for this lab can be purchased from Flinn. Catalog Number Description FB0526 Nutrient Agar, 10 plates LM1006 Escherichia coli AP1227 Applicator Swabs FB1148 Blank sterile swabs

 Safety Precautions After use, agar plates will contain viable microbes. Do not open the plates unnecessarily. Use sterile techniques at all times while handling bacterial cultures. Before disposal, plates should be soaked in a 10% bleach solution or autoclaved. The plates should then be disposed of directly into the garbage. Set a good example of sterile techniques for students when handling culture plates be sure to sterilize work areas before and after handling microbes and have students wash their hands with soap before leaving the laboratory area. Bleach solution is a corrosive liquid, and may cause skin burns. Avoid contact with heat, acids, and organic materials. Isopropyl alcohol is a flammable liquid and is slightly toxic by ingestion and inhalation.