Saddleback Journal of Biology - Saddleback College

Spring 2010 Biology 3B Paper
distribution between the cytoplasm and extracellular
fluid. (Campbell et al., 2008) With such a long
standing and well documented history of
antimicrobial qualities, the objective of the study was
to examine if oregano oil would inhibit the growth of
three bacteria: Escherichia coli, Salmonella
typhimurium, and Staphylococcus aureus. It is
hypothesized that the growth of the bacteria would be
greatly effected the presence of the oil.
Materials and Methods
Forty nutrient agar plates were prepared
using Difco nutrient agar. Three bacteria: Escherichia
coli, Salmonella typhimurium, and Staphylococcus
aureus, were cultured and provided by the
Saddleback Biology Department. Sterile water was
used as the control.
Supplies and methods were completed using
aseptic technique; gloves and eye shield were donned
and all materials used were from sterile packaging or
had been autoclaved. Serological pipettes were used
to transfer 0.3 mL of E. coli to the nutrient agar
plates. A glass rod spreader was used to distribute the
bacteria evenly around the petri dish. After each use,
the glass spreader was dipped in 95% ethanol, passed
through a Bunsen burner flame before being used on
the next agar plate. The procedure was repeated for S.
typhimurium, S. aureus, and water control plates.
Three chad disks were dipped in the oregano
oil and placed onto each agar plate using forceps. The
brand Nature’s Answer alcohol-free oregano oil,
purchased from The Vitamin Shoppe in Mission
Viejo, California, was combined with olive oil and
contained active ingredient Carvacrol at 7.0 mg per
0.2 mL of oil. This dropper bottle was purchased
from The Vitamin Shoppe in Mission Viejo,
California. Forceps were dipped in 95% ethanol and
passed through a Bunsen burner flame before
handling each disk. All agar plates were incubated at
37.0°C for 48 hours at Saddleback College.
Data was collected by measuring the entire
diameter of the chad and area of inhibition.
Measurements were taken using a metric ruler
(millimeters) and values were recorded to the tenths.
Area of inhibition of one chad disk was calculated by
subtracting the chad disk diameter, 7.0 mm, from the
inhibition diameter. The summation of these values
was then divided by the total number (n=30) to obtain
the mean diameter of inhibition. Statistical test
ANOVA was run comparing the bacterial growth to
each other.
Results
The oregano oil had a similar effect on the
mean area of inhibition on each bacterium. An
ANOVA statistical test was run. A significant
difference (p-value of 1.04E-09) was found between
the groups. A Bonferroni post-hoc test provided data
to compare each bacterium to each other. Data was
an MS residual of 14.63211111 and DS residual of
3.0, and a confidence interval of 95%. Compared to
one another the bacteria showed no statistical
significance (p-value > 0.05) (Figure 1).
Diameter of Inhibition (mm)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
S.aureus E.coli S.typhimurium
Figure 1. The comparison of inhibition of growth of bacteria (n=30) Staphylococcus aureus, Escherichia Coli, and
Salmonella typhimurium against oregano (Origanum vulgare) oil (Carvacrol at 7.0 mg per 0.2 mL). Control was
water and showed zero inhibition. P-Value was statistically insignificant (> 0.05) (Bonferroni Correction Test)
and bacteria are graphed with a 95% confidence interval. S.aureus standard error of 0.158832, E.coli standard
error of 0.172239, and S.typhimurium standard error of 0.229767.
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Saddleback Journal of Biology
Spring 2010