Saint Martin’s University
An investigation of bacterial growth in generic versus brand name lotions and shampoos
over a 2 week period
Chelsi Claussen
May 8, 2007
Senior Seminar
Final Draft
Table of Contents
Abstract
1
Introduction
2
Methods
Packaging of Products
Participants
Distribution
Broth Preparation
Participant Study- Bottle and Lid Swabbing
Agar Preparation
Participant Study- Colony Counts
Bacterial Culture Preparation
Laboratory Study
Zone of Inhibition
Statistical Tests
6
6
6
7
8
8
9
10
10
11
11
12
Results
12
12
15
16
Spectrophotometer Testing
Zone of Inhibition
Product Testing
Discussion
17
Acknowledgements
20
Literature Cited
21
2
Abstract
Research was done to test differences in bacterial growth between generic and
brand named shampoos and lotions after two weeks of use. Forty-four Saint Martin’s
volunteers were assigned a shampoo or lotion to use. Spectrophotometer tests were done
to measure optical density and colonies were grown from the used products. Data was
analyzed and some significant differences were found in the lotions. These differences
showed that Avon lotion had a higher level of bacterial contamination in the lotion bottles
and the lotion lids after certain incubation times. No differences in bacterial
contamination were found between either of the shampoos. Lotions and shampoos both
grew bacterial colonies.
3
Introduction
Bacteria are everywhere in society. They are on the toilets we flush, the computer
keyboards we touch, and the beds we sleep in. We clean ourselves and the places we live
to rid ourselves of bacteria and to prevent infections they may cause in the human body.
Some of us do not think that the products we put on our bodies could become
contaminated with a variety of bacteria over time. Contamination is one of the leading
causes for recalls of products bought by consumers (Campana et al., 2006). If
contamination of a product is already a risk while it is in production or on the shelf, the
user also has a possibility of contaminating those products they use over time. How
products are packaged, how often they are used, and how they are stored predict the risk
of user contamination. When we use products such as shampoos and lotions, we may not
consider that these liquids could harbor a variety of microorganisms that could harm us or
cause us to become ill. We expect these products to cleanse and protect our health and
bodies, not infect us with unwanted microorganisms. One way to protect ourselves is to
study the kinds of products we use and the best ways to prevent bacterial growth in them.
In a study by Brannan and Dille (1990), the effects of lid closure and product
packagings were tested to investigate the relationship between the kinds of lids and the
variety and amount of bacterial growth in products. Unpreserved and preserved
shampoos and lotions were placed into bottles with lids with different types of lids. One
type of lid allowed a maximum exposure to the atmosphere while in use, another allowed
for moderate exposure, and the last allowed little to no exposure to the air. The
repackaged products were then distributed to subjects who were told to use them
normally. After the products had been used for 2-3 weeks, they were returned for testing.
4
The tests were done by measuring the amount and variety of bacteria in the product
immediately after return of the samples and again after 7 days of incubation. This study
found that products packaged with wider openings were more likely to become
contaminated with bacteria than those with moderate or small openings (Brannan and
Dille, 1990). This study concluded that unpreserved products became more contaminated
than preserved products (Brannan and Dille, 1990). This study aided in the development
of my hypothesis by showing that products in containers with lids of wider openings will
have the greatest possibility for contamination, and products with more preservatives may
be less likely to grow and develop bacteria. This showed that the packaging of a product
is related to the number of bacteria that contaminated the product.
In a study conducted by Campana et al. (2006), 91 cosmetics were tested to
measure the amount of bacterial growth after 0, 2, 7, 14 and 28 days of use. They tested
these products with a Cosmetics, Toiletries, and Fragrance Association challenge test.
Two strains collected from samples from the 91 products were cultured in nutrient broth
at 37°C for 24 hrs. The samples were then mixed and incubated at room temperature for
0, 3, 7, 14, 21, and 28 days. After these durations, the samples were plated on nutrient
agar, and plates were incubated at 37°C for 24 h. After 24 h, the number of bacterial
colonies were counted. Each product was tested 4 times in this manner. The results
showed that 6-7% of the shampoos contained bacterial contamination while no
contamination was seen in the lotions. The scientists concluded that shampoos can carry
bacteria while in use. The two most common bacteria found in the shampoos were
Staphylococcus warneri and S. epidermidis (Campana et al., 2006). Like my proposed
study, Campana et al. (2006) tested shampoo and lotion products for contamination after
5
different intervals of time using a nutrient agar base. While the Campana et al. study
identified the kinds of bacteria that could grow in the products and the amounts of
bacteria that grew over time, I counted the number of colonies that grew from products
that had been used for 2 weeks.
In a study performed by Okeke and Lamikanra (2001), bacteria in lotions and
creams used in tropical countries were tested for microbes at the time of purchase and
after 14 days of use by a consumer. Forty-nine products were used in this study, 25
creams and 24 lotions. They found many microbes in the creams before and after use;
the most common were Escherichia coli and Pseudomonas aeruginosa. Okeke and
Lamikanra (2001) also created three different types of creams that contained different
preservatives. These creams were injected with bacteria, and incubated in a simulated
tropical environment. After 0, 1, 2, 7, 14, and 28 days, the samples were tested for
microbial growth. The highly preserved products showed no growth and, in some cases,
a decline in the amount of bacteria. The less preserved products showed an increased
amount of the bacteria in the samples (Okeke and Lamikanra, 2001). This study showed
that preservatives within the products had an effect on the quantity of bacterial growth.
In the eyes of many consumers, ingredients in brand name products should be more
effective than generic products (Grassl, 1999). My study tested this assumption.
Nole et al., (2000) conducted a study showing that leave-on-lotions, which are
applied and not washed off, are an effective form of transportation for bacteria.
However, if the lotion contained an active preservative, there was a reduction in the
transfer of bacteria. The main preservative tested in this study was triclosan, a widely
used antibacterial ingredient. Nole and colleagues (2000) compared two lotions, one
6
which contained triclosan and one that did not. In one test, each lotion was placed on
separate agar plates that had already been contaminated with bacteria. The zone of
inhibition, the area where the product inhibited the growth of bacteria, was measured to
determine the effectiveness of the preservative, triclosan. The preservative was shown to
remain effective at inhibiting bacterial growth on the agar plate after 24 h (Nole et al.,
2000). Next, the lotion containing triclosan was applied to the arms of volunteers, and
then a portion of the arm was washed. This was done three times to determine whether
the lotion would remain on the skin to prevent bacterial contamination. After the arm had
been washed three times, the triclosan residue was still apparent (Nole et al., 2000). This
residue could prevent the growth of bacteria on the skin. This supported the
development of my hypothesis by showing that certain ingredients in lotion resulted in
the least amount of bacterial growth while being used by the consumer. The amount of
bacterial growth was also tested using zone of inhibition testing, which I also used in my
research.
Preservatives, ingredients, and packaging all play a part in determining the
amount of bacterial growth in cosmetics. My hypothesis was that a brand name lotion
(Avon™) and shampoo (Pantene™) would have less bacterial growth in the product and
on the bottle than a generic lotion (Dry Skin™) and shampoo (White Rain™) after 2
weeks of normal use by a consumer. The brand named products contained preservatives,
methylparaben in the Avon™ and sodium benzoate in Pantene™, that the generic
products did not. The products were packaged in bottles with the greatest risk for
contamination with twist top lids. After 2 weeks of normal use, products and their
packages were tested for bacterial contamination.
7
Methods
I measured the amount of bacterial growth in three ways. In one test, I measured
the zones of inhibition after my products had been placed on nutrient agar plates that
were inoculated with bacteria. In the second test, participants used pre-bottled shampoos
and lotions normally for two weeks, allowing enough time for bacteria to grow in the
bottles. After this duration of time, the bottles and the lids of the products were swabbed
and incubated in Ward’s Natural Science nutrient broth and tested for total bacterial
content by measuring the optical density using a spectrophotometer. The third test was
done by counting the number of colonies that grew on nutrient agar plates after
inoculating them with shampoo and lotion that was used by participants.
Packaging of the Products
I ordered and obtained all of my shampoo, lotion, and bottles either through eBay
or at Wal-Mart. Once the products were bought, I took them to the lab and measured the
volume to be placed in each bottle. I placed 240 ml of shampoo into each 8 ounce bottle
and 120 ml of lotion into each 4 ounce bottle.
Participants
I submitted a completed Institutional Review Board application for approval by
the board. Once the approval had been given, I recruited 23 participants of the Saint
Martin’s University population to be a part of my study by asking friends and classmates
to participate. I randomly assigned them to groups by allowing the participants to choose
from a number ranging between 2 and 21. After choosing a number, I gave that
participant the bottle with the labeled corresponding number. There were some
participants that only took shampoo or only lotion due to the fact that some could not
8
keep the shampoo in a normal environment, the shower. All participants signed a consent
form that was approved by the Institutional Review Board. After the consent forms had
been signed, I distributed lotions and shampoos in unlabeled, but numbered bottles, to the
participants to ensure it was a blind study. The participants were told to use the products
normally, as they would with their usual everyday shampoo or lotion (Brannan and Dille,
1990).
Distribution
Ten White Rain™ shampoos, 10 Pantene™ shampoos, 10 Dry Skin™ lotions and
10 Avon™ lotions were distributed in the following ways: four control groups were set
up, two half full bottles of each shampoo and each lotion. The control bottles were
placed in an undisturbed, normal environment and left for the duration of the two weeks.
The normal environment for the shampoo was in a shower, and the normal environment
for the lotion was in a room at room temperature (20 °C). This determined the amount of
bacteria that may have already been present in the atmosphere or in the bottles before
distribution. Four treatments were composed of ten participants per group. These
products were packaged in the same way as the controls, except the bottles were filled.
One group was given an 8 oz. bottle of Pantene™, packaged with a twist cap closure to
allow for maximum exposure to bacteria. The second group was given White Rain™ in
the same packaging. The third group received a brand name lotion, Avon™, packaged in
a 4 oz. bottle with a twist cap closure allowing for maximum exposure to bacteria. The
fourth group received the generic lotion, Dry Skin™, packaged the same way as the
brand name lotion. Once the products were distributed, participants were told to use the
9
product normally, as they usually would with their regular shampoo or lotion, for two
weeks. After the two weeks, the products were returned to me for testing.
Broth Preparation
A nutrient broth was needed to incubate swabs of the returned bottles and bottle
lids after two weeks of use. I also would later need broth tubes to incubate used shampoo
product for the colony count testing. I tested 44 shampoo bottles and lids along with 44
lotion bottles and lids at 24, 48, and 72 hours. I also needed to inoculate 48 tubes for
colony counts with product from each bottle used in the study. Therefore, I needed to
make 336 broth tubes. For 336 test tubes to be filled with 15 ml of nutrient broth, 5,040
ml of liquid broth was made by adding 40.32g of powdered broth to 5.04 liters (8g / 1L)
of distilled water and mixed over a hot plate until dissolved. The test tubes were each
filled with 15 ml of broth and autoclaved in the 2540E machine at 121 º C and 15 pounds
per square inch (psi) for 20 minutes. After autoclaving, the samples were removed, caps
were tightened, and the test tubes were put away in the refrigerator for later use.
Participant Study- Bottle and Lid Swabbing
Once the products had been distributed and returned after two weeks of use, I
tested the amount of bacterial growth inside the bottles. This was done by first swabbing
once around the inside of each bottle with a sterilized swab 2 inches from the top. I also
tested the amount of bacterial growth on the bottle lids. This was done by swabbing the
inside of the lid of each bottle with a sterilized swab. These swabs were then placed in
15 ml of autoclaved nutrient broth in sterilized test tubes and placed in the incubator at
37° C to allow for maximum growth of bacteria. A Spectronic20D+ spectrophotometer
was used to indirectly record bacteria levels in the tubes. I first calibrated the
10
spectrophotometer before I tested the broth; I did this by zeroing the control knob while a
cuvette of nutrient broth that once contained a sterilized swab, was in the machine. Next
I placed 3 ml of broth from an incubated swab into a cuvette and placed it into the
spectrophotometer. This device measured the absorption of light through the broth and is
an indirect measure of bacteria present in the liquid (Branson, 2005). The less light
absorbed, the fewer bacteria in the sample and the better the product was at controlling
the growth of bacteria. This was because as the light passed through the liquid it was
either absorbed by the bacteria present or sent through the nutrient broth itself. After
placing the broth into the cuvette I read the spectrophotometer and recorded the values.
The testing was done after 24, 48, and 72 hrs of incubation at 37° C.
Agar Preparation
In order to test the ability of the shampoos and lotions to prevent bacterial growth,
I tested the zones of inhibition of each product and also tested the amount of bacteria by
doing colony counts. I poured 40 nutrient agar plates for the zone of inhibition testing so
that each product could be tested 4 times per plate with ten plates per group. I did this to
increase the sample size for the zone of inhibition rather than just doing the test once for
each product. For the colony counts I poured 132 plates so that product from each bottle,
24 shampoo bottles, and 24 lotion bottles could be tested 3 times each. To make the
Ward’s Natural Science nutrient agar that was used for the lab portion of my study, I
needed to add the powdered agar into 6,240 ml of liquid, 12 ml per Petri plate. I did this
by mixing 143.52 g of nutrient powder with 6,240 ml of distilled water (23g / 1L). Next,
I autoclaved the agar in the 2540E autoclave machine at 121° C and 15 psi for 20 minutes
so that any bacteria or contaminants that may have been present were killed. After the
11
mixture had been autoclaved I poured approximately 12 ml of agar into each Petri plate
and let the plates cool and solidify and then stored them in the refrigerator upside down
so that no condensation would drip onto the agar. The plates were stored there until
further use in the zone of inhibition and colony count testing.
Participant Study- Colony Counts
Another way to test if there were any bacteria in the products distributed to the
participants was to take .15g of the returned product from each bottle and place it into 15
ml of autoclaved nutrient broth. These tubes were labeled accordingly and placed in the
incubator at 37° C for 48 hours to allow for maximum growth of any bacteria that may
have been present in the product. 200 micro liters of the mixture was then placed onto a
pre-made nutrient agar plate. This product was then spread around the plate with a
sterilized L-shaped glass rod. Ten samples were taken from each bottle for a total of 480
samples. These samples were then placed upside down in the incubator at 37° C. The
samples were checked and the number of colonies growing on each plate were counted
and recorded at 24 and 48 hrs.
Bacterial Culture Preparation
In order to use the Pseudomona aeruginosa for my zone of inhibition I first had to
make a main culture of the bacteria that was sent to me. I did this by taking the vial of
bacteria that was ordered from the 1993 Ward’s Natural Science catalog last semester and
added 0.5 ml of the liquid media that was sent with it. I let the dry bacteria soak in the
0.5 ml of media and mixed it together with a pipet. After it had been mixed I soaked a
sterile swab in the bacteria and inoculated an agar slant that was included with my
ordered bacteria (Ward’s, 1993). The rest of the bacteria were then pipetted into a broth
12
tube and both the broth and agar slant were incubated for 96 hrs at 37 ºC. From this main
culture, four autoclaved broth tubes were inoculated with these bacteria and incubated for
96 hrs at 37 ºC.
Laboratory Study
I started the lab portion of the study by inoculating nutrient agar plates with
Pseudomona aeruginosa. I did this by spreading the bacteria lightly over the surface of
the agar with an L-shaped glass rod. This bacteria was chosen because it is known to be
found in shampoos and lotions by prior studies (Lintner and Genet, 1998). After the
inoculated agar had been made, I diluted each of my products to 50% with distilled water
to make the product easier to be placed on and soaked into the filter paper (Brannan et
al., 1987). Once this had been done, a 0.5 inch paper filter disk was dipped half way into
the diluted product and was placed on one of the four corners of the inoculated agar plate,
for a total of four filter paper disks per Petri dish. After the plates had been prepared,
they were placed into an incubator at 37 °C for 24 hrs (Branson, 2005). Each product was
tested 40 times, a total of 10 plates for each product and four filter paper disks per plate.
After 24 hrs, the zone of inhibition was measured in mm with a ruler by looking at it with
the naked eye.
Zone of Inhibition
The zone of inhibition is the area of the inoculated agar where bacteria have not
grown due to a product’s ability to inhibit bacterial growth. The measured area was the
diameter of the inhibited growth of the bacteria including the filter paper disk, which was
covered with product (Branson, 2005).
13
Statistical tests
After the testing was completed, I compared the results of each kind of shampoo
and each kind of lotion to each other by means of an Analysis of Variance test, ANOVA.
The ANOVA test was run through Minitab® (2005), which is a statistical program used
to run tests. If a significant difference was found a Tukey multiple comparisons test was
then done.
Results
Spectrophotometer testing. The optical density was tested from nutrient broth
cultures of bottle and lid swabs taken from products used by participants for two weeks.
One swab was taken from the inside of each bottle and one was taken from each lid. A
total of 48 bottles were tested. These results for these tests are shown in Figures 1-4.
Figure 1 shows the bacterial growth from nutrient broth cultures of swabs taken from lids
of both the generic lotion (Dry Skin™) and the high quality lotion (Avon™) after 24, 48,
and 72 hours of incubation. At 24 hours (F=12.38, d.f.=1, p= 0.002) and 48 hours (F=
7.23, d.f.= 1, p= 0.013) one-way ANOVA tests revealed significant differences in the
amount of bacterial growth between the generic and brand name lotion bottles. However,
at 72 hours (F= 1.32, d.f.=1, p= 0.264) there was no significant difference in the amount
of bacteria in the generic and brand name lotion bottles. The Tukey comparison tests
done through Minitab® (2005), with an individual confidence level (ICL) of 95%
showed that there was a significant difference in growth between the generic and high
quality lotion bottles at 24 and 48 hours, but no significant difference at 72 hours.
14
Absorbance at 686 nm
0.6
0.5
0.4
Dry Skin
0.3
Avon
0.2
0.1
0
24
48
72
Incubation Tim e (h)
Figure 1. Average optical densities of cultures from lotion bottle lids. Twenty-four bottle lids were
swabbed; 12 bottles containing the product Dry Skin™, and 12 bottles containing the Avon™ product. The
optical density of cultures of these swabs was measured after 24, 48, and 72 h. The error bars represent one
standard error.
Figure 2 compares bacterial growth after 24, 48 and 72 hours of incubation from
nutrient broth cultures of swabs taken from the inside of the lotion bottles. Once data
were collected they were analyzed with an ANOVA test showing that there was a
difference in bacterial growth from cultures between generic and brand name lotion
bottles. Results of a Tukey test though Minitab®, with an individual confidence level of
95% show no significant difference in the amount of bacteria after 24 hours (F=0.09,
d.f=1, p=0.762) and 48 hours (F=3.25, d.f=1, p=0.085) hours, but the Avon lotion bottle
swabs were significantly higher in the amount of bacteria after 72 hours (F=8.70, d.f.=1,
p=0.007).
15
Absorbance at 686 nm
1.4
1.2
1
0.8
Dry Skin
0.6
Avon
0.4
0.2
0
24
48
72
Incubation Time (h)
Figure 2. Average optical densities of cultures from lotion bottles. The insides of 24 bottles were
swabbed; 12 bottles containing the product Dry Skin™, and 12 bottles containing the product Avon™. The
optical density of nutrient broth cultures from swabs was tested after 24, 48, and 72 h of incubation. The
error bars represent one standard error.
Figure 3 shows the comparison of bacterial growth from nutrient broth cultures of
lid swabs from generic (White Rain™) and high quality shampoos (Pantene™) after 24,
48, and 72 hours of incubation. The figure shows that after an ANOVA test was
conducted at 24 hours (F=0.98, d.f=1, p=0.333), 48 hours (F=0.82, d.f=1, p=0.375) and
72 hours (F=1.41, d.f=1, p=0.248) hours there were no significant differences in the
amount of bacterial growth. There was also no significant difference in the amount of
bacterial growth from the nutrient broth cultures of shampoo bottle swabs after 24 hours
(F= 3.36, d.f.= 1, p= 0.070), 48 hours (F=3.66, d.f.=1, p=0.069) and 72 hours (F=0.12,
d.f.=1, p=0.735) (Figure 4).
16
Absorbance at 686 nm
0.3
0.25
0.2
White Rain
0.15
Pantene
0.1
0.05
0
24
48
72
Incubation Time (h)
Figure 3. Average optical densities of cultures from shampoo bottle lids. Twenty-four bottle lids were
swabbed; 12 bottles containing the product White Rain™, and 12 bottles containing the product Pantene™.
The optical density of nutrient broth cultures of these swabs was tested after 24, 48, and 72 h of incubation.
The error bars represent one standard error.
Absorbance at 686 nm
0.3
0.25
0.2
White Rain
0.15
Pantene
0.1
0.05
0
24
48
72
Incubation Time (h)
Figure 4. Average optical densities of cultures from shampoo bottle swabs. The inside of 24 bottles were
swabbed; 12 bottles containing the product White Rain™, and 12 bottles containing the product Pantene™.
The optical density of nutrient broth cultures of these swabs was tested after 24, 48, and 72 h of incubation.
The error bars represent one standard error.
Zone of inhibition testing. The zone of inhibition testing showed the
effectiveness of products in inhibiting the growth of the bacteria Pseudomonas
aeuginosa. After testing each product 40 times, the Dry Skin™, Avon™, White Rain™,
17
and Pantene™ after 24 hours had no zones of inhibition. They all had bacteria that grew
over the entire plate.
Product testing. Table 1 shows the results for the products that grew colonies.
After reviewing the data ANOVA tests showed no significant difference in the number of
plates that grew bacterial colonies among the types of lotion and shampoo after 24 hours
(F=1.04, d.f.=1, p=0.310) and 48 hours (F=1.15, d.f.=1, p=0.288).
Table 1. Colony growth from products after 200 micro liters of product from each bottle, A-J, was spread
on nutrient agar plates in replicates of 3. If any of the three replicate plates grew colonies, those bottles in
which grew colonies are marked with an X.
Lotion
Dry Skin™
Control 1
Control 2
A
B
C
D
E
F
G
H
I
J
Avon™
Control 1
Control 2
A
B
C
D
E
F
G
H
I
J
Shampoo
24
HOURS
48
HOURS
White Rain™
Control 1
Control 2
A
B
C
D
E
F
G
H
I
J
Pantene™
Control 1
Control 2
A
B
C
D
E
F
G
H
I
J
1
27
1
53
11
21
109
1
8
20
98
50
1
1
212
2
74
29
1
12
1
18
24
HOURS
48
HOURS
1
1
1
2
2
58
1
1
1
2
Discussion
The results of this two week study show that bacteria grow in all of the products
whether they are brand name or generic name products. The testing shows there was a
higher amount of bacteria on swabs from the lids of bottles containing Avon™ lotion
than the Dry Skin™ lotion after 24 and 48 hours of incubation, but not after 72 hours
(Figure 1). Shampoo and lotion products can be contaminated while in use by the
consumer (Campana et al., 2006). It has been concluded that when people compare
brand name and generic name products that many assume that a brand named product
will have a higher quality (Grassl, 1999.) High quality can be viewed as working better
due to the fact that they may contain more preservatives. This information could
conclude that the brand name products, such as the Pantene™ and Avon™ used in this
study, would allow for less bacterial growth in the bottles that contain them than those of
generic products while in use by the consumer.
When comparing this to my hypothesis that the brand name product would have
less bacterial growth than the generic product, my data failed to support the proposition
because the Avon™ did not have fewer bacteria than the Dry Skin™. This could be
because the Dry Skin™ lotion stuck to the lids of the bottle, while the Avon™ lotion did
not, which may not have allowed the bacteria a place to grow as well as it did in the
Avon™ bottles. This was a problem because optical density is tested by the amount of
light that passes through a liquid. Because lotion was stuck on the sides of the bottles,
when I swabbed them I also obtained lotion on the swab that was then placed in nutrient
broth to be incubated. After incubation the broth was tested by means of optical density,
but because the lotion was present in the liquid it made the absorbance reading of the
19
nutrient broth higher than it should have been. Once the lids were swabbed, the swabs
were placed in test tubes containing nutrient broth and put into the incubator at 37° C, the
bacteria had an adequate place to grow and perhaps once it had enough time, the growth
of bacteria from the Dry Skin swabs grew faster than those bacteria that had already been
swabbed from the Avon™ lids.
When swabbing the inside of the lotion bottle, both the Avon™ and the Dry
Skin™ lotion product clung to the inside of the bottle itself. Therefore, bacteria had the
capability to grow in a similar environment. There was no difference in the amount of
bacteria after the swabs had been incubated for 24 or 48 hours (Figure 2), but there was a
difference after 72 hours. After 72 hours there were more bacteria in the Avon™ lotion
than in the Dry Skin™ lotion (Figure 2). This suggests that the bacteria that were present
in the Avon™ lotion thrived better than those bacteria in the Dry Skin™ lotion after 72
hours of incubation. These results failed to support the original hypothesis, that the brand
named Avon™ would have less bacterial growth than the generic Dry Skin™, because
the Avon™ lotion had more bacteria at 72 hours.
After swabbing the lids and bottles of the Pantene™ and White Rain™ shampoos
and incubating the swabs, no differences between the amount of bacteria were found after
24, 48 or 72 hours of incubation (Figures 3 and 4). These results suggest that
approximately the same amount of bacteria grew in both the high quality brand name and
generic name products. Therefore the higher quality product did not reduce the amount
of bacteria that grew inside or on the lid of the bottle. These results failed to support my
hypothesis because the Pantene™ shampoo did not have a lower amount of bacteria in
the bottle.
20
After two weeks of use the bottles were returned to me and many still had
approximately 75% of the product left. It is possible that bacteria could have had reduced
growth because there was little space available in the bottle and any bacteria that were in
the bottle were diluted by the amount of product. If the bottle had been filled with less
product, more bacteria may have been sampled when pipetted into the nutrient broth.
Also this may have been an adequate amount of product and different results may have
been found if subjects could have used the products for a longer period of time.
After placing the products from the bottles onto nutrient agar plates and
incubating them to allow the maximum amount of growth, the number of bacterial
colonies that were growing on the plates were counted. The results of this show no
difference in the amount of bacteria between either of the shampoos or lotions being
tested. This suggests that bacteria thrived the same in both types of shampoo or lotion,
which failed to support the hypothesis that the brand named products would have less
bacterial growth than the generic named products.
A problem that should be addressed if this study is later replicated is to put less of
the product in the bottles. Two weeks was not enough time to use all the product that
was given to the subjects, and it was difficult to swab the bottles because the lotion or
shampoo was so close to the top. When conducting the swabbing portion of the study,
centrifuging the bottles would have been key to move the product to the bottom of the
bottle, but the centrifuge was not working at the time. In the end this suggests that some
of the numbers from this study were incorrect because lotion or shampoo was present on
the swab when it was placed in the nutrient broth and incubated. To make these numbers
as accurate as possible, when the swabs were taken from the bottle approximately the
21
same amount of product was acquired and placed into the nutrient broth with the swab. It
is also possible, the bacteria that were present inside the bottles were diluted by the large
amount of product that was left. If a smaller amount of product had been used, more
accurate spectrophotometer readings and colony counts could maybe have been obtained.
In the end, we all use products that clean our bodies or rid the world around us of
germs and bacteria. We do this to prevent the spread of diseases and to just live a clean
and healthier life. Little do we know that these products that we trust so much to rid
ourselves of these things could contain bacteria that may eventually cause harm or
disease to us and our family. This study shows that the products we use in our homes can
not always be trusted, and that maybe after a few weeks, our shampoo and lotion bottles
need to be replaced.
Acknowledgements
I would like to give special thanks to Dr. Mary Jo Hartman, Dr. Margaret Olney,
Cheryl Guglielmo, Amber Bridges-Brock, the subjects that participated in my study and
the Saint Martin’s University community.
22
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