The Effect of Sunglass Lenses on the Growth Inhibition of the Bacterium Serratia
marcescens Against Ultraviolet Radiation
Myka Cabuhat, Justin Euperio and Peter Huang
Department of Biological Sciences
Saddleback College
Mission Viejo, CA, 92692
The sun is the primary source of energy, heat, and light, however the sun's energy in
the form of radiation has been shown to be problematic. Too much exposure to UV
radiation raises the risks of diseases including cataracts, macular degeneration, and
cancer, and is also antimicrobial because it damages DNA molecules (Zion, et al., 2006).
Sunglass lenses play a major role in protecting against the effects of UV radiation. In this
study, the growth of Serratia marcescens in nutrient broth tubes was tested with different
sunglass lenses (Gray Polarized, Gray Tint, Transition Gray, Clear UV400) against
exposure to UV radiation. It is predicted that bacterial growth inhibition will not be
significantly different based on lens opacity. Gray polarized (GP) lens culture had 66.26
x 108 ± 6.99 bacterial cells (± se), the gray tint (GT) lens culture had 44.67 x 108 ± 4.81
bacterial cells (± se), the transition gray (GTran) lens culture had 65.33 x 10 8 ± 6.96
bacterial cells (± se), the clear UV400 lens had 28.73 x 108 ± 3.25 bacterial cells (± se),
and the control broth culture had 12.93 x 108 ± 0.91 (±se). The means were compared
using an ANOVA with a Post HOC Bonferroni correction (p=1.90×10-11). The results of
this study supported this hypothesis, as not all lenses were capable of producing
significant growth inhibition.
Introduction
UV radiation has been shown to be both
positive and negative. It is a source of
energy, heat, and light, and is also known
for being a large source of Vitamin D.
However, too much exposure to UV
radiation increases the chance of developing
a wide range of diseases. According to Kuijk
(1991), photochemical damage is induced by
relatively long-term exposure to lower levels
of light in the UV and blue regions of the
spectrum and are thought to initiate
chemical reactions. This UV radiation has
been attributed to the damage of germinal
epithelial cells such as corneal or lens cells
by their interference with and mutagenesis
of DNA (Behar-Cohen, et al., 2013). The
cumulative effects of UV radiation have
therefore been linked to being a cause of
cataracts, keratitis, age-related macular
degeneration and various eye and skin
cancers. However, the use of sunglasses
could greatly decrease these damaging
effects. The purpose of this study is to
determine if levels of bacterial growth are
significantly different between the different
colorations of lenses. The study’s hypothesis
is that there is no significant difference in
bacterial growth post UV radiation based
upon the opacity of the lens.
Materials and Methods
Nutrient broth for bacteria cultures was
prepared by mixing 8.0 g of Criterion
nutrient broth powder with 1.0 L of
deionized water. Test tubes (n=25) were
filled with 10.0 mL of the prepared nutrient
broth. Test tubes for serial dilutions (n=175)
were filled with 9.0 mL of sterile deionized
water using the Integra Biosciences Dose-it
803 auto pipette machine. Both the nutrient
broth tubes and sterile water tubes were
placed in the autoclave to ensure sterility.
The nutrient broth tubes were inoculated
with prepared cultures of Serratia
marcescens via aseptic technique. S.
marcescens was chosen for its pigmentation
and ability to colonize on the cornea, as it is
frequently isolated from lenses of patients
with contact lens-associated corneal
infiltrates (Zhou, et al., 2012). The 25
cultured nutrient broth tubes were separated
into 5 groups of 5 tubes each. Each lens type
(Polarized Gray, Gray Tint, Transition Gray,
Clear UV400) was then placed over their
respective group of culture tubes (n=5 per
lens), while one group of culture tubes were
fully exposed without a lens to serve as a
positive control. All culture tubes were
placed into the Lab Con Co® Ultraviolet
light cabinet and were placed at an optimal
distance of 25-30 cm from the light source.
The culture tubes were then exposed to
Ultraviolet light with a wavelength of 260
nm for a duration of 5 minutes. After
exposure, culture tubes were incubated for
48 hours at 30°C. After the 48 hours
incubation period, each culture tube was
then serially diluted in sterile water (1x107).
Pour plates for colony counts (n=75) were
prepared by aseptically placing 0.1 mL of
each of the culture tube's 107 dilution along
with one full type of liquefied nutrient agar
into Petri dishes marked with the type of
lens used and the dilution factor (107). The
pour plates were then left on the tabletop to
solidify. After the plates had solidified, they
were then inverted and placed into Petri dish
holders and incubated for 48 hours at 30°C
before bacterial counts were performed.
Bacteria counts were performed using the
viable plate count method, which utilizes the
Quebec colony counter (Clark, et al., 2014).
Countable numbers were defined as being
between 0-300 colonies. Viable bacteria in
the original broth culture was calculated
using the following formula: Avg. # of
Colonies x Dilution Factor x Plating
Dilution. Data was transferred to Microsoft
Excel 2007 for data analysis. An analysis of
variance (ANOVA) was used to compare
bacterial colony counts of each lens and the
control. A Post HOC (Bonferroni
Correction) test was then indicated by the pvalue, and implemented to determine if there
was a significant statistical difference
between groups.
Results
On average, the gray polarized (GP) lens
culture had 66.26 x 108 ± 6.99 bacterial cells
(± se), the gray tint (GT) lens culture had
44.67 x 108 ± 4.81 bacterial cells (± se), the
transition gray (GTran) lens culture had
65.33 x 108 ± 6.96 bacterial cells (± se), the
clear UV400 lens had 28.73 x 108 ± 3.25
bacterial cells (± se), and the control broth
culture had 12.93 x 108 ± 0.91 bacterial
cells (±se). The p-value was reported to be
p=1.90×10-11 indicating a significant
difference in Serratia marcescens colonies
between all lenses against control colonies.
A Post Hoc test however, determined no
statistical difference (p>0.05) between the
GP and GTran, GT and GTran, GT and
Clear, and the Clear and Control lenses.
Conversely, a statistical difference (p<0.05)
was found between the GP and GT, GP and
Clear, GP and Control, GT and Control,
GTran and Clear, and GTran and Control
lenses.
Figure 1. Mean number of Serratia marcescens
colonies against the type of lens blocking exposure to
the Ultraviolet light.
Discussion
The opacity of the lens should in theory
block the penetration of Ultraviolet light,
more so with increasing opacity. If that UV
exposure is limited, more bacterial growth
should result as less bacterial DNA is
damaged. DNA synthesis inhibition is
attributed by this damage as UV irradiation
results in the formation of thymine dimers in
polynucleotide chains, ultimately halting
protein translation (Setlow, et al., 1963).
Oxygen radicals are also generated which
can cause lipid peroxidation and protein
modification (Kuijk, 1991). With less
mRNA production and more protein
misfoldings, fewer viable colonies would be
present.
In this experiment however, it was
expected that the different opacities and
types of lenses used would not significantly
alter bacterial growth levels after exposure
to Ultraviolet light. The results of this study
supported this hypothesis, as not all lenses
were capable of producing significant
growth inhibition of Serratia marcescens.
We therefore believe this indicates that
although sunglasses do limit UV penetration
to an extent, that penetration is not highly
affected by the lens type or color, suggesting
all sunglasses to be relatively equal in
protection. Similar results could be
translated from the experiments done by
both Rosenthal, et al. (1988), and Dongre et
al. (2007), as they discovered that UV
protective sunglasses, such as those used in
this experiment, decreased penetration of
UV rays to anywhere between 2-14%, in
comparison to the potential 100%
penetration, granted no natural or superficial
uv light protection. Of course the efficacy of
sunglasses in protecting against UV rays
depends on a number of mechanical factors
such as their size, shape, wearing position,
and reflection from the posterior lens
surface, as well as personal factors such as
latitudinal residency, outdoor vs. indoor
occupations, working in open or reflective
environments (such as sand or water), and
extensive outdoor leisure activities, all of
which can greatly increase exposure
(Rosenthal, et al., 1988). Despite these
factors, the range of protection offered by
sunglasses does not prove all sunglass types
to be significantly effective.
Although significance cannot be
noted between the different lenses, it is
important to still note that there was a
significant difference in bacterial growth in
the broth cultures protected by a lens versus
the control broth culture which was fully
exposed to UV radiation without a lens.
These results prudently signify the
importance
of
wearing
sunglasses
altogether. The importance of this will be
greatly increased in the future as global
warming may introduce more and more UV
radiation on Earth, imminently requiring
similar experiments to be done in order to
engineer more enhanced forms of UV
protection that will maximize the level of
UV radiation attenuation.
Literature Cited
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T., Ortega, P.G., Krutmann, J., PeñaGarcía, P., Reme, C., Wolffsohn, J.S.
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(E-SPF®), a New Ultraviolet Protection
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Acknowledgements
Special thanks to Professor Teh for his time
and patience in assisting with our
experiment and answering any questions we
had. Special thanks to LensCrafters and the
Biological
Sciences
Department
at
Saddleback College for providing us with
the required materials to carry out this
project.
Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s):__ Myka Cabuhat, Justin Euperio and Peter Huang_____
Title:_The Effect of Sunglass Lenses on the Growth Inhibition of the Bacterium Serratia marcescens
Against Ultraviolet Radiation
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.
The experiment compared the effects of UV radiation on bacteria through four different sunglass
lenses and a control group with no lens by looking at bacterial growth on agar. The hypothesis was
that there would be no significant difference in bacterial growth inhibition between the different
lens types. Their results did not support their hypothesis because a significant difference was found
between six comparisons of lenses (determined by a Post-Hoc Bonferroni correction after an
ANOVA test).
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our
current state of knowledge.
The paper had a very thorough materials and methods section with in detail explanations that were
clear and well-written. The results section is also strong as it clearly describes the findings of the
study in an understandable way. However, the introduction and discussion sections are lacking. The
introduction section needs more background information to explain what exactly the project shows
about UV radiation and sunglass lenses and it needs to give some background on the specific
bacteria they chose. Also, the discussion section needs more to explain what this study adds to our
current state of knowledge. As a whole, the paper is well-written (with few grammatical errors),
well organized, and professional.
Technical Criticism
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and minor textual problems. It's not the reviewer's job to copy Edit the paper, mark the manuscript.
Errors have been commented on in comment boxes within the paper itself.
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