1. Assessment of UV Keyboard Sterilizer
Jonathan D. Sexton, M.S.
Charles P. Gerba, Ph.D.
Department of Soil, Water and Environmental Science
University of Arizona
Tucson, Arizona. 85721
June 25, 2008

2. Objective:
The purpose of this study was to evaluate a UV Keyboard Sterilizer against
methicillin resistant Staphylococcus aureus (MRSA), Escherichia coli, MS-2
(bacteriophage), Aspergillus niger.
Methods:
MRSA - An overnight culture of Methicillin resistant Staphylococcus aureus
(MRSA) ATCC 700698 were grown in Trypticase Soy Broth (TSB)(Difco, Sparks,
MD). Bacteria were prepared by centrifugation and resuspension in sterile
physiological saline. This bacterial suspension was used as an inoculum.
E. coli- An overnight culture of E. coli ATCC 25922 were grown in Trypticase
Soy Broth (TSB)(Difco). Bacteria were prepared by centrifugation and
resuspension in sterile physiological saline. This bacterial suspension was used
as an inoculum.
MS-2 - Assay of coliphage MS-2 ATCC 15597-B1 bacteriophage was
accomplished using the double-layer agar technique (Adams, 1952). A colony of
Escherichia coli ATCC 15597 was transferred to Tryptic Soy Broth (TSB) and
grown for 3 hours at 37ºC in a shaking water bath to reach the log growth phase
to serve as host.
A. niger- Grow mold spores on Sabouraud’s agar amended with 50 mg/L
chloramphenicol until they sporulate which will be evident by the formation of
black to dark brown spores on the surface of the mold. Using a pipet, wash the
slants down with sterile saline gently agitating the top surface of the mold, if
necessary to dislodge the spores. Put the saline spore suspension in the
refrigerator until used. Let the spores settle out and pour off the supernatant or
spin down the spore suspension to concentrate the spores.
A piece of acrylic was used to simulate a keyboard. The acrylic surface was
inoculated with 100 µL of the microbial suspension was applied in 10 micro liter
droplets using a micropipetter. After allowing the microbial suspension to air dry
for 30 minutes. The acrylic was then placed in the UV sterilizer and exposed to
UV light for 90 seconds. Another piece of acrylic was inoculated but not exposed
to the UV light to serve as a control. After the exposure time the acrylic was
sampled using cotton-tipped applicator swabs (Becton Dickinson, Sparks, MD).
The swabs were then vortexed for 30 seconds to recover the organisms. The
organisms were then serially diluted and spread plated onto the appropriate
media. MRSA was assayed on Trypticase Soy Agar amended with 5% sheep
blood (Hardy Diagnostics, Mesa, AZ), 0.015 g/L of Nalidixic Acid (Sigma, St.
Louis, MO) and 0.01 g/L of Colistin (Sigma). MRSA was incubated at 37ºC for 48
hours. E. coli was assayed on MacConkey Agar (Hardy Diagnostics) and

3. incubated at 37ºC for 24 hours. A. niger was assayed on Sabouraud Dextrose
Agar amended with chloramphenicol (Hardy Diagnostics) and incubated for 5
days at 37ºC. MS-2 was assayed using the double agar overlay method and
incubated at 37ºC for 24 hours. Tests were performed in triplicate. After
incubation, bacteria colonies were counted and log reduction was calculated
([Initial concentration/Final Concentration] x log = log reduction).
Results and Discussion:
All results are shown in Table 1.
Table 1. Reduction of Organisms by UV Sterilization
Before UV After UV
Percent
Exposure Exposure
Organism (cfu/mL) (cfu/mL) Reduction
MRSA 4.20E+06 <10 >99.999
E. coli 1.20E+06 <10 >99.999
A. niger 1.50E+04 1.22E+03 92.0
MS-2 1.30E+03 <10 >99.9
The UV keyboard sterilizer reduced MRSA and E. coli greater than 99.999%.
MS-2 was reduced by greater than 99.9%, and A. niger was reduced by 92%. It
is possible that the MS-2 could have achieved a higher reduction if the initial titer
were higher. Mold spores are more resistant to desiccation and UV light, which
could account for having less kill than the bacteria. This reduction could be
greater if the contact time is increased or if the organism is brought closer to the
UV light.