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The effect of different disinfectants on sterilizing
the bacterial concentration of Staphylococcus
epidermidis on computer keyboards
Arlen Chen
Spring Valley High School
120 Sparkleberry Lane
Columbia, SC, 29229
1/19/06
Introduction
o Recently, it has been discovered that
potentially harmful bacteria can
survive on computer keyboards and
keyboard covers.
o Some of the bacteria tested in the
studies can cause complicated
abdominal infections, pneumonia,
and different skin infections.
o Therefore, the disinfection of these
bacteria from computer keyboards
must be considered.
Introduction
o Staphylococcus
epidermidis
o Gram-positive, immobile,
grape-like clusters
o Facultative anaerobe
o Ecology / Pathology
o Small, white colonies
o Inhabits skin of healthy
humans
o Only infects
immunocompromised
humans
o Resistant to antibiotics,
antibodies, phagocytosis
http://www.bact.wisc.edu/Bact330/nfS.epidermidis.jpeg
Introduction
o Staphylococcus epidermidis
o Inhabits skin
o Infections
o Skin lesions
o Pneumonia
o Meningitis
o Urinary tract infections
Introduction
o Independent Variables
o Clorox
o Lysol
o Formula 409
o Disinfectant Keywipes
o Dependent Variable
o Staphylococcus epidermidis
colonies left after disinfection
Previous Research
o Even though previous research was
conducted on the survival of bacteria
on keyboards, there has not been
any research conducted on
determining which disinfectant is best
to sterilize the bacteria.
o Therefore, the purpose of this study
was to determine the ability of four
disinfectants to sterilize
Staphylococcus epidermidis on
computer keyboards.
Hypothesis
o Using Clorox for 10 minutes will be the
most effective way of sterilizing the
bacteria.
o Based on the fact that Clorox
contains Clorox and the halogen
chlorine.
Materials
Staphylococcus
epidermidis
Nutrient Agar
Nutrient Broth
Beakers
Petri Dishes
Keyboard Keys
Lysol
Clorox
Formula 409
Disinfectant Keywipes
Incubator
Autoclave
Sterile Cotton Swabs
Sterile Disposable Inoculating
Loops
Hot Plate
Experimental Design Diagram
No
Disinfectant
4 Trials
Lysol
Clorox Formula Disinfectant
409
Keywipes
4 Trials 4 Trials
DV: Growth of bacteria
C:
Time incubated
Time disinfectant is applied
Time bacterium is applied
Bacterium used on keyboards
5 Trials
5 Trials
Methods
o Creation of nutrient agar and broth.
o Staphylococcus epidermidis was
transferred into the nutrient broth
o Broth was spread onto each key.
Methods
o Each disinfectant was sprayed or
wiped on the five keys
o Sterile cotton swabs used to swab the
surface of the key and streaked onto
the corresponding agar plate.
o Once the streaking was completed,
the agar plates were placed into the
incubator at 31ºC for 24 hours.
Results
60
50
40
30
20
10
0
Control
Lysol
Clorox
409
Keywipes
Keywipes
409
Clorox
Lysol
Control
Results
30
25
20
15
10
5
0
Results
x
Control
Lysol
Clorox Formula 409 Disinfectant Keywipes
Trial 1
0
0
2
3
14
Trial 2
43
1
0
5
1
Trial 3
0
2
0
22(1)
44
Trial 4
19
3
1
22
58
53
9
Trial 5
Mean:
StdDev:
15.50
20.40
1.50
1.29
0.75
0.96
21
20.04
25.2
24.51
Results
ANOVA Summary Table
x
d.f.
Disinfectants
Error
Total
4
18
22
Sum of Squares Mean Square
2207
5266
7472
552
310
--------
F
p
1.78 .179
---------
Using the F-distribution table at a significance level
of .05, the critical value (C.V.) is found to be 2.93.
Discussion
o When examining the number of
colonies for each disinfectant, it was
found that there was no significant
difference between the mean
number of colonies at α=0.05.
o Therefore, the experimental
hypothesis was rejected; the
disinfectants did not vary in their
abilities to disinfect Staphylococcus
epidermidis on computer keyboards.
Sources of Error
o Counting errors
o Outliers in the data
o Errors in data analysis.
o Small sample size
Future Research
o Different bacteria
o Have a larger sample size
o Other surfaces
o Other disinfectants
Acknowledgements
o I would like to thank Mr. Soblo for
providing guidance, motivation,
ideas, and advice throughout my
research project, as well as allowing
me to use his class as my lab.
o I would like to thank Ms. McAlpine for
assisting me in ordering materials.
o I would like to thank Ms. Sutton for
providing me with information and
advice.
o I would also like to thank my family
for their support and guidance
throughout my project.
Literature Cited
o
o
o
o
o
o
Adams, D. (2005). Keyboards latest culprit in hospital infections.
AMNews. Retrieved May 2, 2005 from http://www.amaassn.org/amednews/2005/05/02/prl20502.htm
Bates, B. (2005). Computer keyboards act as bacteria reservoir.
Family Practice News 35, 27. Retrieved August 6, 2005, from Health
and Wellness Resource Center.
Hannford, A. (2003 May 19). Key strokes; Mmmmmm; bacteria:
eating at your desk and swapping work stations can seriously
damage your health, discovers an anxious Alex Hannaford. The
Evening Standard (London, England). Retrieved May 2, 2005, from
Custom Newspapers (Infotrac-Gale).
Leichman, A. (2005 January 11). Average office is breeding
ground for germs. Knight Ridder/Tribune Business News Retrieved
May 2, 2005, from Custom Newspapers (Infotrac-Gale).
Marquis, R. (2005). In Microsoft Encarta. Retrieved August 6, 2005,
from
http://encarta.msn.com/encyclopedia_761574409/Bacteria.html
WebMDHealth. (2005). What’s lurking on your computer? Bacteria
can quietly thrive on computer keyboards. Retrieved May 1, 2005,
from
http://my.webmd.com/content/Article/104/107365.htm?pagenum
ber=1
The effect of different disinfectants on sterilizing
the bacterial concentration of Staphylococcus
epidermidis on computer keyboards
Arlen Chen
Spring Valley High School
120 Sparkleberry Lane
Columbia, SC, 29229
1/19/06