EXPERIMENT

This experiment will attempt to determine the effectiveness of various handwashing strategies by measuring the number of bacteria that can be easily removed from the hand after washing.

1. Each student will be assigned one handwashing agent which will be used for the whole experiment. The choices include:

• water
• alcohol
• plain detergent or dish soap
• povidone-iodine
• bar hand soap
• disinfectant solution.

  Notify your instructor if you have any skin allergies to any of these agents.

2. Each student will need two (2) tryptic soy agar (TSA) plates and four (4) sterile swabs. Label the back of your two plates as indicated in the figure and be sure to include your name and washing agent somewhere on the plate.

3. Perform the following to obtain your baseline sample:

• Wet your hands with water.
• Choose one finger on the hand that you don't usually use. This will be your "sample finger".
• Take a sterile swab and swab that finger thoroughly for 15 seconds. Be sure to swab around and under the fingernail.
• Culture this initial "baseline" specimen onto sector "0" of the first TSA plate by lightly but thoroughly streaking the swab across the agar surface in the sector. Don't cross the line into sector "1".
  

4. Now, conduct your investigation as follows:
• Wash thoroughly with your washing agent for two (2) minutes.
• Wash both hands as you normally would and make sure you get underneath fingernails and jewelry.
• If your agent begins to dry out, add more. Your hands should be wet throughout the washing.
• After washing, rinse thoroughly with tap water.
• Don't turn off the water or dry your hands!
• Swab your sample finger as before for 15 seconds and then culture this specimen onto sector "1".
  

5. Repeat step #4 two more times for the 2nd and 3rd cultures on the second TSA plate. Remember not to touch the tap nor dry your hands during the experiment.

6. Incubate your plates at 37^oC until next class period.

EVALUATION

Evaluate your results by comparing the level or amount of growth in sectors 1, 2 and 3 to the growth in sector 0.
Use the following scale:

• (+ +) = growth in sector "0"
• (+) if the growth is less than what you see in sector "0"
• (+ + +) if the growth is more than what you see in sector "0"
• (0) if there are 20 or less colonies in a sector

Tabulate the results on the board and in the following chart:

AGENT	ZERO TIME	1st WASH	2nd WASH	3rd WASH
water
alcohol
detergent
povidone-iodine
bar hand soap
disinfectant sol'n
other __________

HANDWASHING EXPERIMENT - STUDY QUESTIONS

• 1.) Additional Readings: Tortora et. al. Chapter 7 -- look up the handwashing agens that are similar to what we used; Chapter 14 -- normal, transient, commensal flora, symbiosis, opportunism, contact transmission; Chapter 21 -- skin structure and common skin organisms
• 2.) What is the first organism in a newborn's intestine?
• 3.) What is meant by "microbial antagonism"?
• 4.) What is symbiosis, commensalism, mutualism? What is an opportunist? Can E. coli be both a mutualistic organism and an opportunist?
• 5.) What is a nosocomial infection?
• 6.) What is a compromised host? What kinds of things will compromise a patient in a hospital environment?
• 7.) What is meant by "the chain of transmission"? What is a fomite?
• 8.) Is there anything special about the microorganisms in the hospital?
• 9.) Did this experiment teach you anything about how to control the transmission of infectious agents?
• 10.) What are some of the skin diseases caused by Staphylococcus aureus?
• 11.)How about some skin diseases caused by Streptococcus pyogenes?

©2008 by John M. Berestecky
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