Assignment #1 Hand Scrubbing
Running head: ASSIGNMENT #1 HAND SCRUBBING
Effectiveness of Hand Scrubbing Experiment
Submitted by:
Kimberly Nelson -S0241236 L15
A paper submitted in partial fulfilment of the
course requirements on BIO 162
Thomas Graham, M.Sc.
Lethbridge College
February 26, 2008
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Assignment #1 Hand Scrubbing
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Part 1 Experimental Report
Introduction
The purpose of this experiment was to test the effectiveness of hand scrubbing, and the amount
of time needed to be spent in order for it to be effective in decreasing the amount of bacteria on
the hands.
My hypothesis for the hand scrubbing experiment is the person must scrub their hands with soap
and water for three minutes in order for the hand scrub to be effective for decreasing the amount
of bacteria on the hands.
Materials and Methods
The methods and materials can be found in the following references:
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“Effectiveness of Hand Scrubbing” Microbiological Applications Benson, H. J., 7ed.
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Lab #3 notes.
Results
We used five steel basins labelled A-E. “A” was where we rinsed our hands first with no soap,
“B” we rinsed with soap and continued until basin “E.” The water put in each basin was sterile
where we rinsed the hands. In basin “A” you could see many small (1mm) contents floating in
the basin, as we continued to basin “E,” the contents in each bowl were far less, and not as
visible compared to the first couple basins. Once we made our pour plates, we let them sit in
their base until solid and incubated them for 48 hours at 37̊ C. Our group then recorded the count
of all colonies on plates A-E. I observed that the colonies were small, oval shaped clusters of
cells. Some of the cells appeared as little, 1mm, light, creamy yellow dots all over the plates.
Assignment #1 Hand Scrubbing
Others were larger (4mm), white, circular, slimy dots, however, there were far less of these
looking bacteria.
BASIN
A
CFU/Plate
Class Data
Volume (ml) Dilution
Factors (DF)
0.1
10
0.1
10
0.1
10
0.1
10
0.4
2.5
0.4
2.5
0.1
10
0.1
10
0.1
10
0.1
10
810
754
B
681
740
C
728
706
D
224
200
E
324
350
CFU/ml=CFU/Plate x DF
Basin A
DF= 1.0 L / 0.1ml = 10
CFU= 810 x DF (10)=8100
754 x DF (10)=7540
Average= CFU 1 + CFU 2 / 2 = 7820
CFU/ml
8100
7540
6810
7400
1820
1765
2240
2000
3240
3500
Average
CFU/ml
7820
7105
1793
2120
3370
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Assignment #1 Hand Scrubbing
BASIN
CFU/Plate
A
Example Data
Volume (ml) Dilution
Factors (DF)
0.1
10
0.4
2.5
0.1
10
0.2
5
0.1
10
0.1
10
0.1
10
0.2
5
0.1
10
0.4
2.5
67
265
B
192
376
C
38
42
D
102
217
E
35
144
CFU/ml=CFU/Plate x DF
Basin C
DF= 1.0 L / 0.1ml = 10
CFU= 38 x DF (10)= 380
42 x DF (10)= 420
Average= CFU 1 + CFU 2 / 2 = 40
CFU/ml
670
663
1920
1880
380
420
1020
1085
350
360
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Average
CFU/ml
667
1990
400
1053
355
Class and Example Data Average CFU
10000
9000
Avg (CFU / ml)
8000
7000
6000
5000
Exaple Data
4000
Class Data
3000
2000
1000
0
A- 1 min
B- 4 min
C- 7 min
Basin- Time (Min)
D- 10 min
E- 18 min
Assignment #1 Hand Scrubbing
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Discussion
Factors that could have interfered with my results may include:
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Contamination because soap may have got into the basin from the brush or not rinsing the
hands well enough under the tap, as well as not properly sterilizing the tools used to
transfer the bacteria.
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The force used during scrubbing and amount of activity can change per basin
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Where the sample was taken from within the basin
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If the pipette measurements were accurate and all the content from the pipette was
extracted into the plate.
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The incubator may have been too warm or the plates may have been left in too long.
Explanation on what the results mean:
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Contamination of soap in the basin could result with an inaccurate representation of the
bacteria, allowing certain bacteria or microorganisms into the basin. The inoculating tools
to transfer bacteria from one area to another could also not be properly sterilized causing
contaminating, giving an inaccurate growth and growth count.
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The harder the hands were scrubbed the more matter would come off. We cannot get an
exact scrubbing force for each basin which could then lead to an increase or decrease of
bacteria and not give an accurate reading because the hands could be scrubbed harder for
one basin compared to another.
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More bacteria could have settled or be sitting in certain areas of the basin allowing
certain plates to have a higher count depending where the sample was taken from in the
basin. This could allow the count of bacteria to be inaccurate.
Assignment #1 Hand Scrubbing
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If an incubator is set too high of a temperature, it will kill the bacterium that is growing.
If the bacteria are left too long in an incubator, it will dry out and inhibit growth.
Conclusion
In order to maintain the most effective hand scrubbing techniques you must scrub, use soap and
rinse in order to decrease the amount of bacteria on the hands. By washing the hands for at least
three minutes with a brush and soap the majority, but not all of the bacteria will be cleaned of the
hands. Washing the hands is a mandatory protocol before going back to work because scrubbing
helps in the removal of both transient and resident microorganisms that can cause disease or
infection
Part 2 Questions
1. Some microorganisms that are commonly found on the skin of the hands are: Gram-positive
cocci: Staphylococcus, Gram-negative bacilli: Klebsiella-Enterobacter sp., Acinetobacter sp.,
Pseudomonas sp., Proteus-providencia sp. and Yeast. Staphylococcus aureus is the only true
pathogenic organism included in the resident microflora group of skin, and some, but not all,
individuals carry Staphylococcus aureus on their skin. The population of Staphylococcus
epidermidis far out numbers S. aureus on healthy skin
2. The cultural medium used in the hand scrub experiment was veal infusion agar (VIA) pours in
50̊ C water bath. The plates sat until solid and were incubated to grow the organisms isolated
from the hands for 48 hours at 37̊ C.
3. Escherichia coli, S. minus and yeasts can also grow in this medium.
Assignment #1 Hand Scrubbing
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4. I would expect that there will never be ‘zero’ organisms if you continued scrubbing your
hands in this experiment. Organisms and bacteria are everywhere and are always surrounding
you, so I think no matter how hard you scrub there will never be a ‘zero’ count or organisms.
5. The importance of hand scrubbing was first introduced as a clinical procedure in 1846 by
Ignaz Semmelweis when he showed that puerperal fever (childbed fever) cases decreased when
medical students cleaned their hands with lime and chloride before delivering babies. However,
hand washing and disinfection to prevent spread of disease and illness was not practiced until the
later part of the 19th century due to the efforts of Pasteur and Lister. Today it is a routine practice
to clean and disinfect hands before having any contact with patients. Scrubbing helps in the
removal of both transient and resident microorganisms that can cause infection and disease.
6. Basin A and B are usually higher compared to the other basins. Basin B theoretically is
usually a little higher than basin A because soap is used to clean the hands, where in basin A it is
not used. Between basin C and D, C is higher than D because soap is used and it will decrease
the count of the microorganisms as it is used. As well as D is one of the last basins, and most of
the bacteria are most likely scrubbed off and is in one of the previous basins.
7. There is a decrease in the number of bacteria isolated between basin B and C because in basin
B is where soap is first used and it took off a lot of the microorganisms off the hands. When you
scrubbed for basin C, the majority of the bacteria was taken off in the first rinse with soap and
put into basin B. So basin C would have less isolated bacteria because there is less bacteria being
washed off the hands. Also, it could be because between basin A and B, transient bacteria was
washed off. Then between B and C, no bacteria was being washed because transient was gone,
but resident had not started to come off yet. Then between basin C and D is where resident
bacteria would be washed off.
Assignment #1 Hand Scrubbing
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8. Errors that could have occurred in this hand scrubbing experiment could be: contamination
because soap may have got into the basin from the brush or not rinsing the hands well enough
under the tap, as well as not properly sterilizing the tools used to transfer the bacteria. The force
used during scrubbing and amount of activity can change per basin because you cannot get the
same force of scrubbing for each basin. Also, where the sample was taken from in the basin.
Some areas could have more matter settling in certain spots compared to areas with less matter in
the same basin. The pipette measurements may not have been accurate and all the content from
the pipette may not have been extracted into the plate giving an error when it came to bacteria
count. Also, the incubator may have been too warm or the plates may have been left in too long.
This could lead to the bacteria dyeing or inhibiting in the growth process.
9. If I was to design a hand scrubbing protocol using the results from my lab results I would
suggest scrubbing should stop at 3 minutes. Not all of the bacteria is off the hands, however
many people do not wash their hands well. From what I have seen people just do a quick rinse,
so by getting them to scrub their hands with soap for 3 minutes we can decrease the number of
bacteria by just about half. Between basin A and B, transient bacteria was washed off. Then
between B and C, no bacteria was being washed because transient was gone. You can never get a
‘zero’ count of bacteria, so no matter how hard you scrub there will always be bacteria on the
hands, because of this I would make my experiment last 3 minutes.
10. Surgeons use two pairs of gloves even after hand scrubbing to make sure that their hands are
free from contamination. It is impossible to completely remove all the bacteria from the skin,
even with a surgical scrub. This is one reason surgeons wear gloves. The other reason is to
protect themselves from pathogens of patients. Also, it is a two layer protective barrier so that if
substance happens to get into the first glove it will still be sterile because there is another sterile
Assignment #1 Hand Scrubbing
layer underneath. It minimizes the risk of infection to the patient because the surgeon not only
washed their hands but put on two pairs of sterile gloves to help protect their patient from
bacteria.
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