Antimicrobial wipes and their effectiveness on shopping cart handles.
Steven Parrish
Table of contents
Section
Page Number
Introduction
1-6
Materials and Methods
7-8
Results
8-10
Discussion
10-11
Acknowledgements
11-12
Literature Cited
13
1
Abstract:
The emergence of antimicrobial wipes in grocery stores at the entrances by the
shopping carts is relatively new. This study examined the amount of bacteria present on
shopping cart handles at a supermarket that provides antimicrobial wipes and a
supermarket that does not. Cart handles were swabbed and then wiped with antimicrobial
wipe and swabbed again and samples were transported to the lab. After incubation period
of 24 and 48 hours at 37 C levels of bacteria were measured using a spectrophotometer
with absorbency light at 686nm. Results after 24 hours of incubation revealed that
absorbency on average was two times that of the supermarket that did not provide
antimicrobial wipes. Due to possible error, results after 48 hours registered negitive
values.
Bacteria are an important factor in our lives. They can protect us from infection,
disease and maintain overall health, but certain bacteria can be detrimental to humans.
The most common method for transmission of harmful bacteria to humans is due to cross
contamination by humans (Larson, 2001). The lack of sanitation by humans is due to
inadequate hand washing or lack of education on proper hygiene. Humans quite often
come in contact with other humans and subsequently, the objects they touch. At the point
of human to human contact, our skin, hair and clothing are our first line of defense from
harmful bacteria (Courtenay et al., 2005). The more hygienic we are, the less chance we
will infect others with unwanted bacteria and reduce the risk of cross contamination
(Larson, 2001).
A study by Larson et al. (2001) concluded that the hands mainly transmit fecal
and respiratory bacteria. In this study, the home was examined for contamination. Larson
et al. (2001) devised a method to measure cross contamination. The study used two
questionnaires that asked members of the home about their hygiene, food preparation,
2
and recent sicknesses. Larson et al. (2001) also observed the home to view the hygiene,
general cleaning and food preparation of members of the household. As expected,
contamination was found in the home, but most alarming was that the kitchen had more
contamination than the bathroom. The study questioned the frequent use of antimicrobial
agents in our homes and at our jobs. Whether it is the hand soaps or chemical cleaners we
use daily, they can potentially allow us to develop resistance to antimicrobial agents. The
study examined the home environment, testing for various contamination points and
concluded that hygiene begins at home and proper sanitation, such as bathing and hand
washing, is paramount. However, Larson et al. (2001) also suggests that our bacteria are
at risk of developing resistance to antimicrobial products. The authors further note that
resistance to antimicrobial agents is on a case by case basis and further investigation into
resistance is needed. The study touches on cross contamination, the primary focus of my
research. Sanitation is the responsibility of each person and for those who are not
responsible, our only defense may be antimicrobial agents.
It is relatively easy to see how cross contamination can develop. Cross
contamination is mostly achieved by one person’s interaction with another, either by
direct or indirect contact. In an article by Lalla and Dingle (2004), the authors focused on
restaurants and looked at the antibacterial effects of sanitizers, when applied to a generic
cloth compared to using fiber cloths with only water at 75  C. The authors stated in their
study that it is thought that cloths used for cleaning are the source of spreading bacteria.
The authors found that frequent use of sanitizers significantly reduced the amount of
bacteria present on kitchen cloths. However, they also found fiber cloths heated in water
at 75  C were sufficient to eliminate bacteria. This shows that the standard practice of
3
the food industry, which is having clean fiber cloths in sanitized water or water at 75  C,
available to clean cooking utensils and work surfaces, should be applied to the home as
well. Due to my experience in the restaurant industry, It seems that most of transmission
of bacteria from one person to another, is done by touch.
The human hand contains moisture and provides an ideal environment for the
transmission of bacteria. Most bacteria need moisture in order to survive (Lalla and
Dingle, 2004), and unless cooking surfaces and hands are sanitized, there is a good
chance that bacteria are present. We are exposed to bacteria everyday; our skin is the
first line of defense and the first point of contamination. As Lalla and Dingle (2004) note,
it is impossible to rid yourself of all bacteria. With good sanitation practices, it is possible
to limit the amount of exposure to harmful bacteria.
The Center for Disease Control and Prevention (C.D.C) estimate that 325,000
hospitalizations, 5000 deaths, and 73 million sicknesses can be attributed to foodborne
illnesses (Medeirous et al., 2001). Medeiros et al. (2001) studied the proper approach to
food education of the consumer. The authors also researched the appropriate methods to
prevent pathogens from invading our lives and studied their health and financial impact
on the community. Food preparation and service in the home was examined in Canada
and the United States in 81 cities. Standards of proper food handling and service that are
used in restaurants were used to examine the home. The study concluded that following
rules of proper cooking temperatures and proper food handling are essential. Cooling
food items to 40F and below or heating them to 140F and above, within a 2 to 4 hour
time frame, and avoiding cross contamination by keeping cooked food items separate
from raw items, can reduce the incidence of how often foodborne illnesses occur. This
4
was important to my research, as an example of how hygiene and sanitation can correlate
to cross contamination at the supermarket and elsewhere. Cross contamination not only
leads to minor illnesses, but it can also lead to more serious problems.
In a study by Johnson et al. (2005) foodborne pathogens such as antibacterial
resistant strain Escherichia coli were examined. Food items from several supermarkets
were collected, from meat to condiments, and tested for antibacteria resistant E. coli by
using specific cultures and performing disk-diffusion assays. Over 1600 items were tested
and it was found that 27% of the items were contaminated with E. coli. The products that
made up the bulk of the E. coli contamination were poultry, pork and beef items. The
study further showed that a large portion of the items contaminated were the antibacterial
resistant strain of E. coli. The authors concluded that foods in supermarkets are a
prominent vehicle for antibacteria resistant E. coli. This study indirectly relates to my
study, in the way the contamination happened. Contamination starts with initial human
contact and progresses to cross contamination at the supermarket. In my research, I
surmise that it begins mostly from the shopper, starting at the home or work and passed
on at the supermarket. Cross contamination is not only limited to humans but animals as
well.
A similar study by Mitchell and Tauxe (1986) examined Salmonellosis and its
antimicrobial resistant Salmonella strain. They found another aspect of the initial point of
contamination. Molecular biology techniques were used to test the origin of
contamination. The authors found that animals with persistent exposure to antibiotic
drugs were the root cause of the resistant strains of salmonella. These animals were fed
antibiotic drugs, and over time the animals’ bacteria developed a tolerance to the
5
antibiotic properties. This study shows in a different way in which the initial point of
contamination is started. In this case, it begins with the animal. The cross contamination
then begins from the initial product; the animal and is then passed on to the shopper at the
supermarket. Both types of contamination have an equal relationship in that the shopper
at the supermarket furthers the initial contamination. These studies lead me directly into
my research that there are potential points of contamination all around the shopper from
the moment he or she enters the store.
The focus of my study was the local grocery store. Some grocery store chains
have antimicrobial wipes next to their shopping cart storage area as a potential way to
reduce or eliminate harmful bacteria on the carts. It is at these stores where shoppers
come in contact with potentially harmful bacteria. The shopping cart handle is usually the
first thing you touch when you enter a store. This can mean that potentially everything
that all previous shoppers came in contact with is on the cart handle. This also means that
whatever you have come into contact with you will add to the handle as well. When a
person shops at a supermarket, they pick up items that are usually pre-packaged. These
items range from meats to various frozen and miscellaneous items. These items rarely
come into contact with bacteria and therefore, are not as much of a concern as the nonpackaged items. Non-packaged items include the produce items and items from bulk food
bins including nuts, candy, bread, and pastry items. These items are subject to the highest
potential cross contamination. Many people put their hands into the bins to sample
products and search the produce looking for the nicest apple or the freshest head of
lettuce. No matter where the bacteria originate from, cross contamination is a
commonality.
6
These are all good reasons for the addition of antimicrobial wipes at the entrance
of the store, but it doesn’t stop there. Frequent hand washing and cleaning of surfaces in
the home can prevent the original contamination. Antimicrobial wipes should be used
only as a second line of defense.
I hypothesize that the difference in the amount of bacteria between the stores that have
antimicrobial wipes and those who do not have anti microbial wipes will not be
significant. This is due to shoppers not using the available antimicrobial wipes.
Fifty carts from one store with antimicrobial wipes and one without wipes were
swabbed, and each swab was placed in a previously autoclaved test tube. Wiping 50
shopping cart handles from two stores with antimicrobial wipes established a control
group. Each cart handle was then swabbed, and each swab was transferred into a
previously autoclaved test tube. Swabbing of the cart handles was done at two separate
times for groups A, store with the wipes and B store without the wipes. Samples collected
were transferred to the lab where previously autoclaved nutrient broth of 10 ml were
poured into each test tube and incubated for a period of 24 and 48 hours at 37C.
After incubation of 24 and 48 hours, testing for optical density of the bacteria
from the store with and with out antimicrobial wipes were done using a
spectrophotometer in order to establish how much bacteria was present. The results from
24 and 48 hour incubation were then analyzed using an ANOVA test. Then, using
Minitab, a Tukey test was done to compare the individual groups to one another.
MATERIALS AND METHODS
The initial portion of the study involved the amounts of bacteria present on
shopping cart handles, in those stores with antimicrobial wipes and those without
7
antimicrobial wipes. The last portion of my research was the compilation of data analysis
of the data.
The initial phase, data was collected in a two-part process, once for establishment
of amount of bacteria and a second for comparison. In both stores, carts were swabbed
similarly to Warriner et al. (2002), where surfaces were sponged, in order to collect
samples of bacteria on the shopping cart handles. There were approximately 100
shopping carts available and I chose to sample 50. The collection of data was done on a
Tuesday, after the heavy weekend of shopping, in the late evening, when shelves were
being stocked. This was done so customers would not be startled by the collection of
data, and when most of the carts were available for swabbing. Managers had given me
verbal consent to conduct my experiment. Collection of cart handle data began with the
swabbing of the cart handles. A sterile swab was taken out of its protective wrapper and
wiped across the top and bottom of the cart handle. Swabbing was done in the same
manner for all carts. Each swab was transferred into a previously autoclaved test tube. In
order to establish a control, each 50 cart handles were wiped with one antimicrobial sheet
per cart and swabbed again after two to three minutes so to let the handle dry.
Antimicrobial wipes used were provided by the store and are a generic store brand.
Transferring the swabs into empty autoclaved test tubes instead into test tubes containing
autoclaved broth was to avoid bringing test tubes of broth to the store. The test tubes
were stored overnight in a refrigerator at 4.4 C and the transported to the lab. Optical
density was measured using a spectrophotometer, to determine the amount of bacteria
present. Test tubes containing 10 ml of nutrient broth from Cynmar was mixed in the
lab from dry powder with de ionized water and autoclaved at 121 C and 15 psi for 15 to
8
20 minutes in a front loading autoclave unit (Brown, 2005). The collected swabs were
transferred into test tubes, which were incubated for 24 hours at 37C. After the
incubation of 5ml, samples from each test tube were poured into disposable cuvettes and
placed in the spectrophotometer. Once the cuvette had been placed in the
spectrophotometer, the wavelength was set to 686 nm (Brown, 2005). The
spectrophotometer was set to zero and then blanked with a sample containing a sterile
swab and nutrient broth that was incubated for 24 hours. The spectrophotometer was then
set to zero and ready to read 100% (Brown, 2005). A single beam of light was sent
through the sample and a reading determined how much light was absorbed by the
sample. Bacteria absorb light, so the more light absorbed, the greater amount of bacteria.
The remainder of each sample was incubated an additional 24 hours and tested in the
same manner. The need for an additional 24 hours of incubation was done in case
something happened in the 24-hour period of incubation. The storage of samples after
they were collected for a period of 12 hours should not effect the normal levels of loss of
bacteria since bacteria such as E. coli has lasted up to eleven days on surfaces (Michaels,
2002). The last part of my research involves the actual comparison of data.
Two types of analysis were used in my study. The first analysis conducted was a
one way ANOVA test between the store with the antimicrobial wipe (A) and the store
without the antimicrobial wipe (B). This was done to determine the statistical difference
between data A and data B. Secondly using Minitab 2005 an Tukey test was performed
to give a confidence interval and determine what difference there are between the two
groups of data.
RESULTS
9
Results were obtained by swabbing grocery cart handles in two different stores.
Fifty cart handles from each store were swabbed before and after wiping the cart handle
with an antimicrobial sheet at each store. I also conducted a brief count of shoppers who
upon entering the store used the wipes provided and I found that it was approximately 1
out of every ten shoppers. Figure 1 shows store A, which provides antimicrobial wipes
and store B, which does not provide antimicrobial wipes. Each store had a control group
established by wiping all cart handles with an antimicrobial wipe. Results of the data
show that when wiping the carts with antimicrobial sheets both store A and store B
registered negitive values. Results also revealed that store A had less than half the
amount of bacteria levels as store B.
10
Absorbance at 686 nm
0.14
0.12
0.1
Store A
0.08
Store B
0.06
0.04
0.02
0
24 hrs
Control - 24
hrs
48 hrs
Control - 48
hrs
Figure 1. Group A is the store with antimicrobial wipes and group B is store without antimicrobial wipes.
24 and 48-hours refers to an incubation period of swabs in nutrient broth at 37C. Control refers to carts
that have been wiped with antimicrobial sheets and then swabbed. At 48 hours of incubation there were no
values for store A. Store B registered only two absorption values out of 50 samples. Error bars represent
one standard deviation.
.
An ANOVA test was performed and showed a statistically significant difference
between the absorbance of samples from cart handles from store A and store B after 24
hours of incubation at 37 C (F= 98.6; DF= 7; p= 0.0005). The results of a Tukey
multiple comparisons test at 95% confidence interval showed significant differences
between group A at 24 hours and group B at 24 hours, with group B having higher levels
of bacterial growth overall.
Discussion
The results of my study did not support my hypothesis that the shopping cart
handles in the grocery store with antimicrobial wipes would have a similar level of
bacteria on the handles as in the grocery store without antimicrobial wipes. Samples from
store A and B were incubated at 42C for 24 hours and 48 hours and tested using a
11
spectrophotometer. At 48 hours of incubation, a problem developed with the samples.
While testing of the 48-hour samples was conducted in the same manner as the 24-hour
samples, the spectrophotometer measured zero absorbance, with the exception of two
samples. I cannot explain this result. I expected that bacteria levels would increase from
the 24-hour incubation. Perhaps the spectrophotometer was not working properly, or I
made a mistake in zeroing and/or blanking the machine. This was unfortunate and
possibly could have been avoided by seeking advice from my professors who may been
able to solve the problem. I did, however, find that levels of bacteria at 24 hours of
incubation in the store A with antimicrobial wipes were about half the absorbency as
store B without antimicrobial wipes. The standard error bars show that the variance
between the data was similar between store A and B.
I hypothesized that even though store A had antimicrobial wipes available most
people would not use them. This, in turn, would mean that the amounts of bacteria on the
cart handles in both stores would be at similar levels. The data did not support this
hypothesis. The results suggest that the large difference in absorbency between store A
and store B could be contributed to the use of antimicrobial wipes. The low level of use
of antimicrobial wipes does not seem to support the conclusion that the wipe use is
responsible for the lower bacteria amounts. It could be that a small amount of shoppers
using the wipes is sufficient to bring bacteria levels down. It also could be that the total
amount of shoppers at the store B is larger than store A, but when looking at the amount
of traffic at the two stores this does not seem to be the case. Store A seems to have a
larger amount of traffic than store B. It is education of the consumer that is needed to
combat potential food borne illnesses (Medeiros et al. 2001). Even though antimicrobial
12
wipes are present at store A, the general public does not necessarily understand their
importance. In retrospect I should have used a larger sample of 100 carts and added
several stores to my test. This could have revealed why there was a significant difference
between bacterial levels on shopping cart handles at store A and B, even though use of
the antimicrobial wipes was limited. Further studies are needed to determine whether
antimicrobial sheets should be added to other areas in the store. Due to the fact that food
items in the store also can be contaminated with bacteria (Johnson et al. 2005).
In conclusion my results did not show that the bacteria levels were similar, it did
show that the store with antimicrobial wipes had far less bacteria on shopping cart
handles than the store that did not provide antimicrobial wipes. Using antimicrobial
wipes may be a way to reduce our exposure to harmful bacteria. As other studies in this
area begin to reveal their findings it shouldn’t be long before all stores decide to make
antimicrobial wipes available to their customers.
Acknowledgments
I would like to thank Kathy Gratias for without her help and support this would
not have been an easy task to complete. I would also like to thank Professors Dr. Hartman
and Dr. Olney for their continued support and direction. I would like to give a special
thanks to Cheryl Guglielmo for her support with equipment and supplies and last but not
least my Biology peers.
13
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