Saddleback Journal of Biology - Saddleback College

Spring 2010 Biology 3B Paper
Introduction
Aromatic plants, such as Rosemary,
Lavender, Oregano, and Thyme have long been
valued for the medicinal and aromatic uses of their
essential oil extractions. In addition, a number of
studies undertaken in the last twenty five years have
looked at the antibacterial properties these plants
possess. The bird species, blue tit (Cyanistes
caerulas) has been found to include pieces of
aromatic plants amongst its normal nest building
material (Blondel et al. 2009). Upon examination of
the effect of these plants on the bacteria present on
the blue tits, it was found that the plants significantly
altered the structure of the observed bacterial
communities specifically in regards to reducing the
density of colonies among hatchlings (Blondel et al.
2009). Variability in antibacterial activity has also
been noted in these plants due to a variance in
concentration of essential oils specifically in regards
to ice nucleation active bacteria (Karamanoli et al.,
2004). In regards to the effects of these plants on
specific bacterial strains, the aromatic plant basil
(Ocimum basillicum) has been shown to be effective
in inhibiting the growth of E coli. (Lopez et al.,
2005). Essential oils appear to derive their
antibacterial effect from their unique chemical
makeup. Each single, pure essential oil consists of
several, sometimes hundreds of distinct natural
chemicals. Essential oils, like all organic compounds,
are made up of hydrocarbon molecules and can
further be classified as terpenes, alcohols, esters,
aldehydes, ketones and phenols. The primary
components known for their antibacterial activity are
Terpene hydrocarbons such as Sesquiterpenes.
Also, there are a few oxygenated compounds known
as phenols. These components have great antiseptic,
anti-bacterial and disinfectant qualities and also have
greatly stimulating therapeutic properties.
Relatively few studies have directly looked
at the variance in effect that different essential oil
extracts from these aromatic plants have on bacterial
growth. The objective of this study was to observe
the amount of growth inhibition of Escheridia coli.
from the application of Lavender and Rosemary
essential oils and whether the two differed
significantly in their inhibition ability. It was
hypothesized that both groups would significantly
inhibit bacterial growth and that they would
significantly vary between each other in the amount
of inhibition
minutes. Three, single hole punch chads of filter
paper were prepared for each Petri dish for a total of
90, these were subsequently autoclaved for forty five
minutes. 20mL of Escherichia coli, E.coli.
(precultured in the microbiology lab a few days prior)
was distributed in 0.5mL increments to each dish in a
lawn spread using a sterile spreader and standard
procedure aseptic techniques, left over E. coli was
disposed of properly. The 30 dishes were split into
three groups: the control group, the rosemary group,
and the lavender group. Three chads were placed on
each dish using tweezers. Control group chads were
dipped in water, whereas rosemary and lavender
group chads were dipped in essential oil extracts of
rosemary and lavender respectively. Oil extracts were
sterilized via boiling and standard procedure Aseptic
techniques were followed in transferring the chads to
dish. All groups were incubated for 48 hours at a
temperature of 37° Celsius. Upon removal from
incubation, growth inhibition was measured as the
diameter of E. coli absence across the center of the
chads.
Results
Before evaluating the data, the diameter
length of the Chad was subtracted from each
measured zone of inhibition in order to get an
accurate measurement. The average zone of
inhibition on E.coli between the three groups was
analyzed for comparison. The rosemary group had
the greatest average growth inhibition at 2.91 mm ±
.414 (± S.E.M) with the lavender group close behind
at 2.45mm ± .546 (± S.E.M). As expected the control
group had the smallest average, .14 mm ± .070 (±
S.E.M) (Figure 1). Although the rosemary group had
the largest average zone of inhibition, as seen in
figure 1, it was found to have no statistical difference
when compared to the lavender group (p= 4.2 x 10 -1 ,
ANOVA). However, when the rosemary group was
examined against the control group there was a
significant statistical difference (p= 3.2 x 10 -4 ,
ANOVA). The results were also similar when the
lavender group was compared to the control (p=3.0 x
10 -4 , ANOVA).
Materials and Methods
1L of agar medium (Criterion Dehydrated Culture
Media) was prepared and autoclaved for forty five
minutes. The agar was then distributed evenly to 30
petri dishes and allowed to cool for a period of forty
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Saddleback Journal of Biology
Spring 2010