18: ANTISEPTICS AND DISINFECTANTS
- Page ID
- 157086
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- Define disinfectants, antiseptics, and antibiotics, and explain their proper applications.
- Analyze your experimental results to determine which agents were most successful at controlling microbial growth.
BACKGROUND
Unlike antibiotics, which are used internally to treat infections, disinfectants (chemicals used to kill microorganisms on external surfaces) are applied to objects and surfaces outside the body. A special type of disinfectant is called an antiseptic (a disinfectant that is safe to use on human skin). Disinfectants and antiseptics are among the most important tools that make modern surgery possible—alongside effective anesthesia (a method for preventing pain during procedures).
Before these tools were developed, surgery was considered a last resort. It was generally used only for emergencies such as repairing traumatic injuries, sewing up wounds, or amputating limbs that could not be saved. Infections after surgery were often fatal, making most surgical attempts extremely risky. During wartime, many soldiers died not from their wounds but from the infections that followed. Even minor cuts from knives or bullets could turn deadly once an infection set in. In fact, it was not unusual for people to die from the infection of a simple scratch or abrasion.
Before germ theory was well understood, people relied on a variety of techniques to try to prevent infection—some more effective than others. Surprisingly, a few traditional remedies were actually useful. Certain herbs and spices, alcohol, and powdered sulfur all have antimicrobial properties. When used consistently, these substances could reduce the risk of infection.
A major turning point in infection control came when Florence Nightingale introduced the routine use of hot water and soap in the care of wounded soldiers. This simple practice led to a dramatic drop in infection and death rates and marked the beginning of modern antiseptic technique.
Some of the same compounds used to prevent wound infections were also used to preserve food. Before refrigeration, food would quickly spoil as microbial cultures multiplied. To slow this growth and prevent food poisoning (illness caused by ingesting food contaminated with harmful microorganisms), people used salt, sugar, acids, alcohol, and spices. These substances helped suppress or kill bacteria and fungi, acting as simple antiseptics or disinfectants both on the body and in food.
MATERIALS (Per Group of 4)
4 Nutrient agar plate
4 Pure cultures
4 Related disinfectants (spices, cosmetics, toothpastes, household cleaners etc.)
2 Cell spreaders
2 Jars of alcohol
2 Turn tables
4 Sterile 1.0 ml pipets
16 Sterile filter paper disks
4 Small beakers
METHODS/PROCEDURES
Choose and Plan Your Test Compound
1. As a group, decide on four compounds to test that are related in purpose.
✔ Examples: Four different herbs, four brands of mouthwash, or four types of household cleaners.
✘ Avoid unrelated items (e.g., comparing mouthwash to a surface disinfectant).
2. Choose something your group finds interesting—you’ll be more engaged in the results.
Inoculate Your Agar Plate
3. Obtain your assigned bacterial culture (a liquid suspension of bacteria).
4. Use a sterile pipette or dropper to place about 0.3–0.5 mL of the culture onto an agar plate.
5. Spread the bacteria evenly across the surface using a metal rod that has been flamed and cooled.
6. Each student in your group should use a different bacterium but test the same four compounds.
7. Share results to compare how each compound affects different bacteria.
Apply the Test Compounds
8. Label the bottom of your agar plate to identify the position of each disc.
9. If your compound is solid:
a. Use flamed forceps to pick up a sterile paper disc.
b. Gently touch the disc to the solid compound.
c. Tap lightly to remove any excess material.
d. Place the disc onto the surface of the inoculated plate.
10. If your compound is liquid:
a. Pour a small amount of the liquid into the container lid or a clean watch glass.
b. Use flamed forceps to pick up a sterile disc.
c. Dip the disc into the liquid.
d. Place the disc onto the surface of the agar.
11. Apply all four compounds using the same technique so your results are consistent and
comparable.
12. Double-check that your plate is labeled correctly to match each disc’s location.
13. Carefully carry your plate to the incubator.
14. Place the plate in the incubator agar side down to keep the discs in place and prevent
condensation from dripping on the agar.
Print a hard copy to bring to lab (PDF).
👉 If you are filling this out on a digital iPad or tablet please note put your name here and take a screen shot.
You are also welcome to print the PDF and turn in a physical copy of the following.
Exercise #:23 Antiseptics and Disinfectants
NAME ______________________
EXPECTATIONS
What four compounds did your team choose to test? List each compound and include any specific brand names or sources if applicable.
Why did your group think these compounds might have disinfectant or antimicrobial properties?
Explain your reasoning.
Which compound do you predict will be the most effective at inhibiting bacterial growth?
Explain why you made this prediction.
RESULTS
Organism tested ____________________________________
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Tested Compound |
Diameter Cleared |
Susceptible or Resistant |
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Organism tested ____________________________________
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Tested Compound |
Diameter Cleared |
Susceptible or Resistant |
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Organism tested ______________________________________
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Tested Compound |
Diameter Cleared |
Susceptible or Resistant |
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Organism tested ______________________________________
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Diameter Cleared |
Susceptible or Resistant |
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CONCLUSIONS
1. After examining the plates for all four bacteria, did any of the compounds appear effective at suppressing bacterial growth?
2. Were the most effective compounds the ones you predicted would work best? Explain your answer and include any surprises.
3. Did any of the compounds work against some bacteria but not others? If so, which compounds were selective, and which bacteria were affected?
4. Was one of the four bacteria generally more resistant to all the compounds tested? If yes, identify the bacterium and describe what you observed.