This document discusses the effectiveness of hand washing in reducing bacterial contamination. It begins by discussing the historical discovery of hand washing in disease prevention. It then describes an experiment where fluorescent dye is used to show that proper hand washing with soap for 20 seconds reduces bacteria on the hands, as seen under UV light. The document outlines a procedure where agar plates are used to culture bacteria from fingertips that are unwashed, washed with water only, washed with soap and water, and sanitized. It demonstrates that washing with soap and water for 40 seconds or more is most effective at reducing bacterial growth.

1. The Effect of Hand Washing
On Bacterial Contamination
Yousef Elshrek

2. • Effectiveness of Hand Washing
• The discovery of the importance of hand and skin surface disinfection
in disease prevention is credited to Semmelweiss at Vienna general
Hospital in 1846.
• Semmelweiss established a policy of hand washing that resulted in a
drop in the death rate due to puerperal sepsis from 12% to 1.2% in one
year.
• Although the skin in never completely sterilized the transient and
normal flora can be significantly reduced by prolonged scrubbing with
soap.

3. • Micro-organisms are found
everywhere, in the environment, on
surfaces in the air and on the human
body.
• Correct hand washing is the single most
effective technique that prevents the
transmission of micro-organisms either
directly or indirectly to others.
• It is essential to show that the hand-
washing method does in fact just
remove micro-organisms from skin.
• To test the hand washing technique, fluorescent dye is applied to the hands prior to
washing.
https://microbiologyitc.weebly.com/uploads/2/4/1/8/24180446/8030141.jpg
https://microbiologyitc.weebly.com/uploads/2/4/1/8/24180446/6568458.jpg
Fig. (1) Microbial contamination for finger dab lab test
• Following washing the hands are examined under UV light for any traces of dye.
• Compare your handwashing with the diagram that shows commonly missed area

4. • MATERIALS
1. Hand soap
2. Nutrient agar plates
3. Hand sanitizer
• PROCEDURE
1. Label 6 the nutrient agar plate into 1 through 6.
2. Plate 1 is negative control. Do not touch it and attempt not to pass your hands inside this plate as
you complete the exercise.
3. Touch agar in plate 2 with unwashed four fingertips. This will be the positive control.
4. Rinse your hands with just tap water for 20 sec. Dry your hands and touch four fingertips to plate
5. Wash your hands with tap water and liquid soap for 20 sec. Dry your hands and touch four
fingertips in the plate 4.
6. Wash your hands with tap water, soap for 20 sec. and sanitize them. Dry your hands and touch four
fingertips in the plate 5.
7. Incubate the plate at 37 C for 24 hrs.
8. Examine the plates for the relative abundance and diversity of growth.
9. Record your results below.

5. RESULTS
• Plate shows a negative control result.
Fig. (1) negative control
University of Georgia Cooperative Extension Bulletin 693

6. • positive control
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Fig. (3) Place unwashed fingertips on nutrient agar plate number 1
Dirty fingers touch agar

7. • Results after incubation period you will see bacterial growth after 24
hours due to contamination of unwashed hands
• The dirty, unwashed fingers contained so many bacteria that the areas
they touched on the agar plate were a mass of colonies.
Unwashed fingers after 24 hours
Fig. (4) bacterial growth after 24 hours due to contamination of unwashed hands
University of Georgia Cooperative Extension Bulletin 693

8. Fig. (5) bacterial growth after 24 hours due to
contamination of washed hands with water only.
• Bacterial growth after 24 hours due to contamination of rinsed hands. Washed hands
with water only for 20 sec.
University of Georgia Cooperative Extension Bulletin 693 3 Food

9. • Wash hands with tap water and liquid soap for 20 sec.
Fig. (6) Fingertips after a 20-second wash with soap and water
• Washing the hands with soap and water for 20 seconds reduced the number of
bacteria, but it was not long enough removing them all.
University of Georgia Cooperative Extension Bulletin 693

10. Fig. (7) Fingertips after an additional
20- second wash with soap and water
• After the hands were washed with soap and water for another 20 seconds, the number of
bacteria decreased even more.
University of Georgia Cooperative Extension Bulletin 693
• These photos show that washing your hands
with soap and water for at least 40 seconds
will reduce the number of bacteria on your
hands.
• Washing them for a full minute works even
better.
• Even though removing all bacteria is
impossible with soap and water alone, the
important thing is to reduce the number of
transient bacteria on your hands.
• Always be sure to wash your hands thoroughly
for at least 40 seconds before you handle food

11. • Wash your hands with tap water, soap for 20 sec. and sanitized.
• No bacteria grew on the agar plate after the fingers were dipped in a sanitizing solution.
• The bacteria may or may not have been killed, but the sanitizer stopped their growth.
• Of course, some people may not be able to use a sanitizing solution because it may
irritate their skin.
Fig (8) Fingertips after using a sanitizing solution
University of Georgia Cooperative Extension Bulletin 693

12. • A sample of liquid soap spread onto nutrient agar and a swab from a bar of solid soap also
spread onto nutrient agar.
Fig.(9) The effect liquid and solid soap on bacterial growth
https://microbiologysociety.org/uploads/assets/d4b19ff7-150c-4b4f-9cb2f560c1e35d1f/600x397_highestperformance_/4.j
• Why do you think that the
solid soap (kept by the sink
and handled regularly) had
more bacteria living on it than
the liquid soap (kept in a
dispenser, so not handled)
which had none?
• You may be interested to know
that while soaps do not kill
microbes, they can be quite a
good medium for them to grow
on!
• Soaps are not designed to kill microbes.
• They help to wash them of your skin, better than
water alone

13. Fig. (10) Effect of a sanitizing solution on sneeze germs
This photo illustrates the effect of sanitizing agents on bacteria. An agar plate was sneezed
on, and then a drop of sanitizing solution was put in the center of the plate. Bacteria grew in
the area not touched by the sanitizer.
University of Georgia Cooperative Extension Bulletin 693

14. • References
1. https://microbiologysociety.org/uploads/assets/d4b19ff7-150c-4b4f-
9cb2f560c1e35d1f/600x397_highestperformance_/4.jpg
2. The University of Georgia, cooperative extension. Food, hands and,
bacteria. Extension Bulletin 693
3. www.chilledfood.org › wp-content › uploads › 2015/07