How strong does a disinfectant need to be to stop bacteria from growing? You prepare five concentrations of disinfectant ranging from 10% to 50%. Filter paper disks soaked in each solution are placed on agar plates streaked with E. coli.
After 24 hours in an incubator, you measure the zone of inhibition (the clear ring where bacteria cannot grow) around each disk. Higher concentrations produce larger clear zones.
Hypothesis
The hypothesis is that the lower the concentration of disinfectant used, the higher the level of bacterial resistance.
The Kirby-Bauer disk diffusion test also reveals how concentration affects a disinfectant's germ-killing power. You prepare five solutions ranging from 10% to 50%, soak filter paper disks in each, and place them on agar plates streaked with E. coli. After 24 hours in an incubator, the zone of inhibition — the clear ring where bacteria cannot grow — around each disk shows how far that concentration stopped growth. Higher concentrations produce larger clear zones, demonstrating that the strength of the solution determines how far it stops germs from spreading.
How strong does a disinfectant need to be to stop E. coli from growing? You prepare five concentrations ranging from 10% to 50%, soak filter paper disks in each solution, and place them on agar plates streaked with the bacteria. After 24 hours in an incubator, you measure the zone of inhibition — the clear ring where bacteria cannot grow — around each disk. Higher concentrations produce larger clear zones, revealing the point at which concentration becomes strong enough to stop this common bacterium.
Method & Materials
You will prepare different concentrations of disinfectant, inoculate a Petri dish with bacteria, and measure the zone of inhibition around the bacteria.
You will need a disinfectant, water, 5 Petri dishes, nutrient agar, E. coli culture, syringe, sterile cotton swab, goggles, gloves, pincers, cellophane tape, incubator, alcohol wipes, 5 50 ml beakers, 5 filter paper disks, stirrer, and marker.
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The results showed that the diameter of the zone of inhibition decreased as the concentration of the disinfectant decreased. This suggests that the bacteria did not develop immunity to the disinfectant.
Why do this project?
This science project is interesting because it explores how bacteria can develop resistance to disinfectants, which is an important topic in the field of microbiology.
Also Consider
Variations to consider include using a different type of bacteria, changing the temperature of the incubator, and using a different disinfectant.
Full project details
Additional information and source material for this project are available below.
