3: DECONTAMINATION
- Page ID
- 157062
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- Observe and compare microbial growth on nutrient agar plates collected from different surfaces before and after handwashing and disinfection to evaluate the effectiveness of basic hygiene practices.
- Recognize the role of consistent handwashing and surface disinfection in minimizing microbial transmission.
BACKGROUND
Microorganisms are everywhere—including on our skin and the surfaces we touch daily. While many of these microorganisms are harmless or even beneficial, others have the potential to cause disease, especially when hygiene is neglected.
In addition, although many surfaces may appear visibly clean, they often harbor a diverse population of microorganisms. These organisms are typically undetectable without specialized tools or growth conditions, yet they persist on skin, objects, and in our surrounding environment.
This exercise is designed to visually demonstrate the presence of microorganisms on human hands and laboratory surfaces by comparing microbial growth under different conditions: prior to and following handwashing, and before and after surface disinfection. When these microorganisms are transferred to nutrient agar plates and incubated, many will multiply to form colonies allowing for direct observation of their growth.
While nutrient agar supports the growth of a wide range of bacterial species, it does not provide optimal conditions for all microorganisms. Thus, the colonies observed will represent only a subset of the total microbial population present on a given surface. Nevertheless, comparing growth between “clean” and “dirty” samples provides valuable insight into the effectiveness of basic hygiene and disinfection practices.
After completing this exercise, it is essential that all students practice proper hygiene protocols at the beginning and end of every class. Washing your hands and disinfecting your workspace not only helps maintain the integrity of your experiments but also reinforces habits that are critical in any health-related field.
MATERIALS (Per Group of Four)
4 nutrient agar plates
2 sterile swabs
1 tube of sterile water
1 lab table disinfectant
6 paper towel squares
Antibacterial hand soap
METHODS/PROCEDURES
Each student in the group chooses one of the four conditions below:
DIRTY HANDS - Student 1
- Label the bottom of the plate (example label below)
- Open the Petri dish just enough to gently rub the fingertips of one hand across the entire surface of the agar.
- Switch hands and repeat the process using the other hand, rubbing over the same plate.
- Close the lid and set the plate aside.
DIRTY BENCH - Student 2
- Dip a sterile swab into a tube of sterile water.
- Rub the moistened swab over an area of the lab bench that has not been disinfected, preferably one that appears dusty or has not been recently cleaned.
- Partially open the Petri dish labeled DIRTY BENCH.
- Gently rub the swab over the entire surface of the agar, rotating the swab slightly to ensure full contact.
- Close the lid and set the plate aside.
- Throw the swab in the trash.
CLEAN HANDS - Student 3
- Wash both hands thoroughly with antibacterial soap for at least 20 seconds (Yes, count). Pay special attention to fingertips and around the nails.
- Do NOT use a paper towel. Allow hands to air dry completely until no longer dripping.
- Once hands are air dried, ask a classmate to open the Petri dish labeled CLEAN HANDS (this is the only time a classmate will help you with the lid).
- Gently rub the fingertips of both hands one at a time over the surface of the agar.
- Close the lid and set the plate aside.
CLEAN BENCH – Student 4
- The fourth student should apply a generous amount of disinfectant to the lab bench surface.
- Use a clean paper towel to spread the disinfectant across the entire bench area.
- Allow the disinfectant to sit for 3 minutes
- Dip a sterile swab into the sterile water tube then swab the cleaned bench surface thoroughly.
- Partially open the Petri dish labeled CLEAN BENCH.
- Gently rub the swab over the surface of the agar, rotating the swab to ensure even coverage.
- Close the lid and set the plate aside.
After all four plates are inoculated:
- Place all four plates in the 30°C incubator, agar side up.
- Incubate until the next lab period.
🔷 Reminder: From this point forward, all students must wash their hands with antiseptic soap and disinfect their lab benches at both the beginning and end of every lab session.
The following is to be completed during lab then turned in on Canvas as a PDF
*If you are using an iPad or tablet you will need to take screen shots of your competed work, save the screenshots as one PDF then submit them on Canvas by the due date designated on Canvas.
*You can also print out the entire exercise to bring to lab with you. If you choose to complete the lab on paper, take pictures of the completed results and conclusions sections only, save them as one PDF, then submit to Canvas by the due date designated on Canvas.
DECONTAMINATION
NAME ______________________
EXPECTATIONS
Do you expect to see microbial growth on any of the plates? Explain your reasoning.
RESULTS:
Using colored pencils draw what you observe on the plates after incubation.
Remember to properly label each drawing.
CONCLUSIONS:
1. Based on your observations, how effective were the disinfectants at eliminating microbes on the bench and hands?
2. If one or both plates, inoculated from the bench (or table) showed no visible microbial growth after incubation, does this mean the bench (or table) was sterile? Why or why not?
3. Describe two possible reasons why bacteria present on the surface of your hands might fail to grow into colonies when inoculated onto the agar plate.
4. Many commercials for disinfectants, toothpaste, and similar products claim to kill 99.9% of germs. How might companies use factors like temperature, growth conditions, or nutrient availability to design tests that make their products appear more effective than they actually are? Explain your reasoning.