“Do you know how to wash your hands?” I asked one student this question before the start of a sanitation lab, and she looked at me like, “Are you kidding me”? Well it seems so simple, that you would think that everyone knows how to do it. But how many of us do? Not only should we know how to wash our hands but also when to wash our hands. The CDC recommends that in order to prevent the spread of germs during the COVID-19 pandemic, we should wash our hands with soap and water for at least 20 seconds. But do we need to scrub that long? Would 5 seconds or 10 seconds be just as effective? What if we sanitize our hands? Do we need to wash them that long if at all? Shanks and Peteroy-Kelly (2009) reported that university students spend an average of 4.87 seconds washing their hands. Borchgrevink et al (2013) found that among 3,749 people, men washed their hands for an average of 6.27 seconds and women 7.07 seconds. So, are they doing enough to get their hands squeaky clean? In this experiment, we hypothesize that washing our hands for less than 20 seconds is fine as long as we sanitize after we wash.

Materials

  1. Palmolive liquid hand soap
  2. 79% iso-propyl alcohol (sanitizer)
  3. Commercial disinfectant
  4. Fan
  5. Nutrient agar plate
  6. Incubator

Procedure

  1. Clear your lab surface of any books of other materials on it
  2. Use a commercial disinfectant to spray the surface and wipe with a paper towel
  3. Keeping the plate closed and upside down, use a marker to draw a line through the center of the base, dividing the plate into two halves
  4. Label one side “before” and one side “after”
  5. Turn the plate right side up and partly remove the cover (just enough to uncover the side that is marked “before”)
  6. Using your index finger on your dominant hand, run it lightly, in a zig-zag pattern, over half of the agar plate labeled “before”
  7. Cover the plate again
  8. Using a 1 ml pipette, collect 1 ml of liquid soap and apply it to your hands
  9. Wash your hands at the lab sink for 5 or 20 minutes (your instructor will assign you to your group based on Table 1). Note: Do not touch the tap to turn it on or off. Your lab partner will do so for you
  10. After you are done washing, have your lab partner dispense 1 ml of sanitizer in your hands
  11. Use a rubbing action to thoroughly apply sanitizer all over your hands including all fingers and between fingers
  12. now, place your hands in front of a fan to dry them
  13. Again, using your nondominant hand, remove the lid from the agar plate to expose the side that is marked “after”
  14. Lightly run your finger over that side of the plate in a zig-zag pattern as before
  15. Cover and incubate the plate at 37oC for 24 hours (place in the incubator up side down)
  16. Your instructor will remove the Petri dish for you and place it in a refrigerator until you return for the next lab
  17. When you come back, observe your Petri dish and answer the questions in the lab assessment

Use disinfectant to clean table top
Sanitizer and hand soap

Nutrient agar
Nutrient agar preparation procedure

Marked petri dish
Use finger to transfer bacteria

Table. Handwashing treatments

Treatment Number of Participants
Wash hands for 5 seconds – Sanitize Afterwards (hold for 30 seconds before fan drying5
Wash hands for 5 seconds – DO NOT Sanitize 5
Wash Hands for 20 seconds – DO NOT Sanitize 5

Lab Assessment

  1. Count and record the total number of colonies you see on each half of the plate (5 points)
  2. Describe the morphological structure of the colonies on both sides (5 points)
  3. What conclusions can you draw from your observations? (5 points)

References

  1. Borchgrevink Carl P., Cha JaeMin, & Kim SeungHyun. (2013). Hand Washing Practices in a College Town EnvironmentJournal of Environmental Health75(8), 18–25.
  2. Shanks, C. R., & Peteroy-Kelly, M. A. (2009). Research Article: Analysis of Antimicrobial Resistance in Bacteria Found at Various Sites on Surfaces in an Urban University. Bios3, 105. https://doi.org/10.1893/011.080.0301
Courtney Simons
Administrator
Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.
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