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THE ANTIBIOTIC ACTIVITY OF VARIOUS NATURAL FOOD ITEMS
Hanan El and Austin Weld
Department of Biological Science
Saddleback College
Mission Viejo, CA, 92692
In recent years, antibiotic resistance in bacteria is on the rise. As a result, alternate
methods to combat pathogenic bacteria must be examined. Cinnamon oil, garlic, roasted
garlic, lemon oil, habanero, onion, and honey have been shown to have antibiotic activity
and were compared in this study. Cinnamon oil was predicted to have the greatest
antibiotic activity. The antibiotic activities of these food items were compared using the
disk diffusion method with 50.0 µL of Staphylococcus aureus lawn spread onto trypic soy
agar plates. Filter paper disks containing 10.0 µL of each item were added to the plates and
the zone of inhibition was measured compared to water. The plates were then incubated for
48 hours at 37°C. A significant difference was shown between the groups (p= 6.54 x 10-41,
ANOVA and Bonferoni Correction). Cinnamon oil had a mean zone of inhibition of 16.12 ±
1.08 mm (±SEM, N=10), which was significantly greater than all other groups. Garlic had a
mean zone of inhibition of 7.72 ± 0.24 mm (±SEM, N=10), which was significantly greater
than all others except cinnamon oil and honey. Honey had a mean zone of inhibition of 9.96
± 0.52 mm (±SEM, N=10), which was significantly greater than all others except cinnamon
oil and garlic. Although previous literature suggested antibacterial activity in lemon oil,
habanero, roasted garlic, and onion, no significant antibiotic activity was observed. This
suggests a potential use of cinnamon oil, garlic, and honey as antibiotic agents.
Introduction
In recent years, the presence of antibiotic-resistance
genes in bacteria is on the rise. Much of this can be
attributed to misuse and overprescription of antibiotics
and antimicrobial agents, the use of antibiotics in farm
animals to increase growth rate, and the ability of
antibiotic resistant genes to travel long distances due to
mass transportation (Lowy 2003). Therefore, it is of
interest to investigate new compounds and ways of
controlling disease-causing bacteria. In addition, with
an increasing public interest in natural products,
naturally occurring compounds in common food items
are
of
particular
interest.
For centuries, essential oils have been used in
alternate medicine, and many have been shown to have
antimicrobial effects. In the study conducted by Ott and
Morris (2008), lemon oil was found to be one of the
strongest of several antimicrobial oils. The mechanism
by which citrus oils such as lemon oil acts is
incompletely understood; however, it is believed that it
is due to the aldehyde citral or lemonel, which has two
stereoisomers: neral, the Z-isomer and geranial, the Eisomer. These compounds contain a carbonyl group act
as alkylating agents to bind cellular nucleophilic
groups, rendering them inactive causing damage to
bacterial cells (Ott and Morris 2008).
Geranial
Neral
Another natural product, garlic (Allium
sativum) is the most famous food with antimicrobial
activity. In a study by Chikwem et. al. (2008), aqueous
raw garlic extract was shown to have significant
inhibitory effects against both Staphylococcus aureus
and Salmonella typhimurium. However, interestingly,
garlic extract which was heated had significantly
reduced antimicrobial properties. Garlic’s inhibitory
effect was brought about by a thiosulphinate molecule
called allicin, which protects the garlic itself from
bacterial attack as it grows. Allicin is capable of
rapidly penetrating into cells through their cell
membrane and attack the sulfur (SH) groups of
enzymes and proteins to alter their function (Jonkers et
al. 1998).
Allicin
Hot peppers from the Capsciumb genus also
have suggested antimicrobial properties. A study by
Koffi-Nevry et. al. (2012) suggests that extracts from
the fruits of the bell pepper plants Capsicum annuum
and Capsicum frutescens were effective antimicrobials
against Vibrio chlorea, Staphylococcus aureus, and
Salmonella typhimurium. The chemical responsible for
the antimicrobial properties of plants from the
Capsicum genus is capsaicin. Furthermore, Wei et al.
(2006) found that the concentration of capsaicin in the
sample was shown to dramatically affect the
antibacterial activity, with concentrations lower than
0.0125 mg/mL having no effect.
Capsaicin
A study by Elnima et al. (1983) tested both
garlic and onion extracts against various gram-positive
and gram-negative bacteria and found both to have
antimicrobial effects. However, garlic was significantly
stronger and a 10% garlic mouth wash solution was
shown to reduce the number of oral bacteria. In onion,
the antimicrobial activity was found to be mainly
produced by a flavonoid called quercetin (Lee 2010).
Quercetin
Honey has also been shown to have
antimicrobial properties. Interestingly, it was initially
thought that the high sugar content may be responsible
for these antimicrobial activities; however, when honey
was compared against artificially constructed honey
produced from a combination of sucrose, maltose,
fructose, glucose, and deionized water, honey had a
significantly higher antimicrobial affect than the
artificial honey, suggesting the presence of a different
antimicrobial compound causing the effect (Cooper et.
al. 2002). These other compounds are mainly hydrogen
peroxide, but the high osmolarity, phytochemicals,
such as methylglyoxal were found to play a roll
(Mandal and Mandal 2011).
Cinnamon oil and its active ingredient,
cinnamaldehyde, have also been shown in several
studies to have antimicrobial effects on the bacteria
Escherichia coli and on various biofilms (de Oliveira
et al. 2012 and Hong et al. 2013). The inhibitory effect
of cinnamaldehyde on bacteria has been suggested to
be due to its detrimental effect on oxidative
phosphorylation, mainly involving the electron
transport chain, preventing the production of ATP (de
Oliveira et al. 2012).
Cinnamaldehyde
In this study, a variety of common, natural
food items that have been shown in past studies to have
antimicrobial products, including garlic, habanero
(Capsicum chinense), onion, honey, lemon oil, and
cinnamon oil, were surveyed by the disk diffusion
method for their effectiveness on Staphylococcus
aureus to determine which is the most effective.
Cinnamon oil was expected to have the largest zone of
inhibition due to a study by Chaundhari et al. (2012)
which showed cinnamon oil to have the largest zone of
inhibition out of nine different essential oils.
Materials and Methods
Garlic (Allium sativum), roasted garlic, habanero
(Capsicum chinense), onion (Allium cepa), honey,
lemon oil (Citrus Limon), cinnamon oil (Cinnamomum
cassia), water, and Staphylococcus aureus were used in
this study. Garlic, habanero, onion, honey, lemon oil,
and cinnamon oil were purchased at Mothers Market in
Irvine, CA. Twenty tryptic soy agar plates were made
on Saturday, November 16, 2013 at 10:10 A.M.
Extracts of garlic, roasted garlic, habanero, and onion
were prepared at 10:00 P.M. in Hanan’s kitchen, the
night before the study was condusted. Two cloves of
raw garlic and 2 mL of sterile deionized water were
blended until it became a liquid solution. Two cloves
of roasted garlic were prepared at 177°C for 20
minutes, and the roasted garlic cloves and 2 mL of
sterile deionized water were blended until it became a
liquid. Two habanero peppers and 2 mL of sterile
deionized water were blended until it became a liquid.
A piece of onion and 2 mL of deionized water were
blended until it became a liquid solution. Honey, lemon
oil and cinnamon oil were already in a liquid state.
Garlic extract, habanero extract, onion extract, honey,
lemon oil and cinnamon oil were aseptically transferred
into sterile test tubes.
The experiment began on Friday November
22, 2013 at 10:30 A.M. Aseptic technique was used
throughout the experiment. Each agar plate was
divided into four sections. Twenty tryptic soy agar
plates were lawn spread with Staphylococcus aureus.
Sterile filter disks were placed onto each section of the
agar plates for a total of 80 samples, 10 for each group.
For the control, 10 µL of sterile deionized water was
pipetted onto each sterile filter disk for a total of 10
samples. 10 µL of garlic extract, roasted garlic extract,
habanero extract, onion extract, honey, lemon oil, and
cinnamon oil were pipetted onto 10 different sterile
filter disks each, for a total of 70 samples. All 20 agar
plates were placed into a 37˚C incubator for 48 hours.
A ruler was used to measure the zone of inhibition
produced from each sample in millimeters.
Results
The mean zone of inhibition of cinnamon oil was 16.12
± 1.08 mm (±SEM, N=10). The mean zone of
inhibition of garlic was 7.72 ± 0.24 mm (±SEM,
N=10). The mean zone of inhibition of roasted garlic
was 0.00 ± 0.00 mm (±SEM, N=10). The mean zone of
inhibition of honey was 9.96 ± 0.52 mm (±SEM,
N=10). The mean zone of inhibition of lemon oil was
1.03 ± 0.12 mm (±SEM, N=10). The mean zone of
inhibition of habanero was 0.40 ± 0.06 mm (±SEM,
N=10). The mean zone of inhibition of onion was 0.00
± 0.00 mm (±SEM, N=10). A significant difference
was observed between the eight groups (p= 6.54 x 1041
, ANOVA and Bonferoni Correction). A post-hoc
comparison showed cinnamon oil had a significantly
larger zone of inhibition than all other groups. Garlic
and Honey had a significantly greater zone of
inhibition than all other groups except cinnamon oil;
however, there was no significant difference observed
between garlic and honey’s zone of inhibition. These
data are shown in Figure 1.
Figure 1. Mean zone of inhibition radius of the water,
cinnamon oil, honey, garlic, roasted garlic, lemon oil,
habanero, and onion (n=10). There was a significant
difference between the groups (p= 6.54 x 10-41).
Cinnamon oil had a significantly larger zone of
inhibition than all other groups. Honey had a
significantly larger zone of inhibition than all groups
except cinnamon oil and was not significantly different
from garlic. Garlic had a significantly larger zone of
inhibition than all groups except cinnamon oil, but was
not significantly different form honey.
Discussion
The results of the experiment support the hypothesis
that cinnamon oil will have the greatest zone of
inhibition. Cinnamon oil had a significantly greater
zone of inhibition than all other food items tested.
The results for cinnamon oil, garlic, and
honey were consistent with previous studies that
showed significant antibiotic activity in cinnamon (de
Oliveira et al. 2012 and Hong et al. 2013), garlic
(Chikwem et. al. 2008 and Jonkers et al. 1983), and
honey (Cooper et. al. 2002 and Mandal and Mandal
2011). Honey had a greater zone of inhibition than
garlic, but this was not significant.
However, contrary to past research, lemon oil,
habanero, onion, and roasted garlic did not have
significant antibacterial activity. Lemon oil had a slight
zone of inhibition, but it was not significant, which is
in opposition to the study by Ott and Morris (2008),
which showed lemon oil to have significant antibiotic
properties, even surpassing various other essential oils.
Surprisingly, habanero showed no significant
antibacterial activity. This is inconsistent with KoffiNevry et. al. (2012) and Wei et al. (2006)’s studies.
Koffi-Nevry et. al. (2012)’s study showed that different
peppers have different capsaicin content. It is very
possible that habanero may have a lower capsaicin
content than other hot peppers. Also, since we added
water to the mix, it may have caused the capsaicin
content to be diluted below the minimum inhibitory
concentration (MIC). Future research could be done
using habanero peppers without water and producing a
more concentrated solution.
Onion showed no zone of inhibition, which is
in contrast to Elnima et al. (1983), which showed that,
although onion was less effective than garlic, it still
had significant antibacterial activity. The results were
also in contrast to the study by Lee (2010) which
suggested significant antibacterial activity. It is
possible that adding water to the extraction mix also
diluted onion past its MIC. Future experiments could
use undiluted onion extra.
Our results for roasted garlic agree with the
study by Chikwem et. al. (2008) that showed a
significant reduction in antibiotic activity of roasted
garlic versus raw garlic, however, our results did not
show any significant antibiotic activities, which is in
contrast to their study. It is possible that the water
played a part, or the garlic may have been roasted for a
longer period of time or at a different temperature,
causing it to lose more of its antibiotic activity.
Because cinnamon oil, garlic, and honey
showed significant antibacterial activity, there is a
potential application of these items in antibiotics and
antimicrobial agents. These compounds may have a use
as inexpensive and effective mouthwashes to combat
oral bacteria. They could have applications against
antibiotic resistant strains of Staphylococcus aureus.
For example, topical creams could be produced that
contain these compounds to fight bacterial infections
on wounds and staph infections. In modern times, with
the increasing prevalence of antibiotic resistance,
exploring alternative products with antibiotic properties
is extremely important.
annuum and Capsicum frutescens. International
Journal of Food Properties. Vol. 15: p 961-971.
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