The use of medicinal plants as a source for relief and illness is ancient and
well documented in the written documents of the early civilization in China,
India and the near east, but it is without question an art as old as mankind
(Mahesh and Satish, 2008).
The potential of higher plants as source for drugs is still largely unexplored.
Among the estimated 250,000-500,000 plant species, only a small percentage has
been investigated phytochemically and the fraction submitted to biological or
pharmacological screening is even smaller (Uniyal et
al., 2006; Mahesh and Satish, 2008).
Historically, pharmacological screening of compounds of natural or synthetic
origin has been the source of countless therapeutic agents. Random screening
as tool in discovering new biologically active molecules has been most productive
in the area of antibiotics. Even now, contrary to common belief drugs from higher
plants continue to play an important role in modern medicine. Medicinal plants
represent a rich source of antimicrobial agents (Uniyal
et al., 2006; Mahesh and Satish, 2008).
Although, hundreds of plant species have been tested for antimicrobial properties,
the vast majority of have not been thoroughly evaluated including cinnamon and
thyme plants (Govindarajan et al., 2006; Mahesh
and Satish, 2008).
Cinnamon (Cinnamomum cassia) is a medicinal plant that posses antimicrobial
properties and shown to inhibit the growth of many pathogens such as B. cereus
(Hoque et al., 2007) and Helicobacter
pylori (Zarchil and Babaei, 2006). The oil of thyme
and its different components are becoming increasingly popular as a naturally
occurring antimicrobial and also as an antioxidant agent (Zarchil
and Babaei, 2006). Thyme showed broad antibacterial activity by inhibiting
the growth of both gram-positive and gram-negative bacteria.
Recently, medicinal plant extracts were developed and proposed for use in food
as natural antimicrobials (Hoque et al., 2007).
However, little study has been done on the effects of plant extracts including
cinnamon and thyme against many food borne diseases and pathogens. The present
study was conduced to screen the effect of cinnamon and thyme extracts against
5 common food borne pathogens.
MATERIALS AND METHODS
Plant materials and microorganisms: This study was done at Ohio
University Zanesville, Ohio, USA between October 12th, 2008 and February
22nd, 2009. Medicinal plants were obtained from Medicinal Plant Teaching
Laboratory at Ohio University Zanesville, Ohio, USA. These plants have
previously been reported to have antibacterial activity against different
bacterial pathogens. Five bacterial pathogens (Bacillus subtilis,
Enterobacter aeruginosa, Escherichia coli, Staphylococcus
aureus, and Staphylococcus epidermidis) were obtained from
Microbiology Teaching Laboratory Collection at Ohio University Zanesville,
These bacteria were selected as these are common pathogens that cause
many food borne diseases.
Preparation of extracts: One liter of an 80% ethanol extraction
fluid was mixed with 100 g of powdered plant material. The mixtures were
kept for 2-5 days in tightly sealed vessels at room temperature at 22°C,
protected from sunlight and mixed several times daily. This mixture is
filtered through muslin cloth.
The extracted liquid was filtered using Whatman No.1 filter paper and
the filtrates were then evaporated to dryness under reduced pressure to
remove the ethanol. Extract was then weighed and stored at 22°C for
Antimicrobial assay: Inhibition of microbial growth was tested by using
the paper disc agar diffusion method (Kirby-Bauer Method; Drago
et al., 1999). In order to detect potential antimicrobial activity
in the plant extracts, entire surface of 20 mL muller hinton agar plate was
inoculated with the culture of bacteria and the paper discs (diameter 5 mm which
absorbs 10-12 μg). The paper discs were soaked in each of the test solutions
containing different extract solutions at varying concentrations (100, 250,
500, 750 μg mL-1) as well as the standard antibiotic solution
(Erythromycin) and the control-blank (sterile water discs) were placed separately
in each quarter of the plate under aseptic conditions. Multiple plates were
(three replications) done for each of the extract. The plates were then maintained
at room temperature for 1 h allowing for diffusion of the solution. All plates
were then incubated at 37°C for 24 h and the zones of inhibition were subsequently
measured in mm in all three replicates using measuring scale and the average
of the three measurements was calculated (Mukherjee et
Determination of minimum inhibitory concentration: MIC of cinnamon and
thyme extracts was calculated using plate dilution method. Taking different
concentrations (100, 250, 500 and 750 μg mL-1) of each plant
extract against 0.1 mL of 10-4 inoculum dilution prepared from 24
h incubated culture of the test microorganism into sterile a sterile plate followed
by pouring of 20 mL Muller Hinton agar medium. In this study, the MIC was the
lowest concentration of plant extracts that exhibited no growth of microorganism
by visual reading. Each experiment was done in triplicates along with positive
and negative controls (Ghosh et al., 2008).
The cinnamon extract at (250, 500 and 750 μg mL-1) concentrations
showed antibacterial activity against Bacillus subtilis, Enterobacter
aeruginosa, Escherichia coli, Staphylococcus aureus
and Staphylococcus epidermidis.
||Antibacterial activity of specific concentration (250 μg
mL-1) of medicinal plant extracts (IZD in mm)
The range of the zone of inhibition was 19 to 29 mm (Table
1). The thyme extract at the same concentrations also exhibited antibacterial
activity against Bacillus subtilis, Enterobacter aeruginosa,
Escherichia coli, Staphylococcus aureus and Staphylococcus
epidermidis. The range of the zone of inhibition was 17 to 28 mm (Table
1). The MIC of cinnamon and thyme extracts against all tested strains
were found to be 250 μg mL-1.
Plants are important source of potentially useful structures for the development
of new chemotherapeutic agents. The first step towards this goal is the in
vitro antibacterial activity assay (Valero and Salmeron,
2003; Zarchil and Babaei, 2006). Many reports are
available on the antiviral, antibacterial, antifungal, anthelmintic, antimolluscal
and anti-inflammatory properties of plants (Kone et al.,
2004; Ghosh et al., 2008). Some of these
observations have helped in identifying the active principle responsible for
such activities and in the developing drugs for the therapeutic use in human
beings (Mahesh and Satish, 2008).
This study shows that extracts of cinnamon and thyme produce effective antibacterial
activity against both gram negative and gram positive food borne pathogens.
Results of this study confirmed the observation of earlier studies by Zarchil
and Babaei (2006).
The cinnamon extract was found to be effective against Escherichia coli
and Staphylococcus aureus. This effect is in agreement with other recent
studies (Yuste and Fung, 2004; Hoque
et al., 2007). In this study the thyme extract showed effective antibacterial
activity against all tested pathogens including Escherichia coli and
Staphylococcus aureus. This result supports the findings of
Dursun et al. (2003), Nevas et al. (2004),
Solomakos et al. (2008) and Friedman
et al. (2006). This study is the first to report the antimicrobial
activity of cinnamon and thyme against Bacillus subtilis, Enterobacter
aeruginosa and Staphylococcus epidermidis collectively.
The current results are very promising and suggest that Cinnamomum
cassia and Thymus vulgaris are beneficial to human health,
having the potential to be used for medical purposes and to be utilized
as anti-bacterial additives in food products.
I thank Ohio University Zanesville for funding this project.