Antimicrobial Activity of Ethanolic Extracts of Ocimum basilicum leaf from Saudi Arabia
Essential oils or volatile oils from medicinal plants have potentially very strong antimicrobial activities for control of pathogenic microorganisms. Ocimum basilicum is one of the medicinal plants which are widely used as sources of extracts with strong antibacterial and antioxidant properties. In this study, the leaf extract of Ocimum basilicum was tested for its antibacterial activity against some human pathogenic bacteria (Staphylococcus aureus and Escherichia coli). Antimicrobial activity test was carried out by using the hole-plate diffusion method. Plant materials were dried and extracted with 95% ethanol. The tested extract showed very strong antimicrobial activity against both strains. The antimicrobial activity was evaluated by measuring the zone of inhibition. The strongest inhibition activity was observed against E. coli (21 mm zone) at 200 mg mL-1 of leaf extract followed by Staphylococcus aureus which showed 16 mm inhibition zone at 200 mg mL-1 of leaf extract. Physical properties of the extract of Ocimum basilicum were evaluated. The color of the extract is greenish, has intense scent, density is 0.937 g cm-3 at 25°C, refractive index is 1.489 and specific gravity is 0.887.
Received: November 02, 2012;
Accepted: January 16, 2013;
Published: July 01, 2013
Ocimum basilicum or Al-Rehan (in Arabic) is a well-known medicinal plant
which has received a great deal of attention over the past few decades around
the world. It belongs to the Lamiaceae family of floral plants usually producing
white-purple flowers (Daneshian et al., 2009).
Extracts of Ocimum basilicum having strong antibacterial and antioxidant
properties are widely used for medicinal purposes. Plant parts and essential
oils from Ocimum plants are used as spices and flavors for many food products
and effective drugs in folk medicine (Sacchetti et al.,
2004; Jirovetz et al., 2003).
Many medicinal plants which produce antioxidants, antibacterial, antiviral
and fungicidal agents have gained popularity in recent years. Extracts from
Ocimum basilicum have shown strong inhibitory effects on HIV-1 reverse
transcriptase and platelets aggregation (Yamasaki et
al., 1998; Okazaki et al., 1998). These
extracts are also a rich source of flavor compounds and volatile oils which
possess compounds that contain antimicrobial activities (Yamasaki
et al., 1998; Wannissorn et al., 2005).
Some parts of sweet basil such as leaves and flowers are used as carminative,
galactogogue, stomachic and antispasmodic medicinal plants in folk medicine
(Marwat et al., 2011).
Due to random and wide usage of antibiotics in the treatment of infectious
diseases, a multiple drug resistance against pathogenic microorganisms has been
developed in recent years (Davies, 1994; Service,
1995). One of the best ways to solve this problem, is to look for new therapeutic
agents from plants which contain antimicrobial activities against these pathogenic
microorganisms (Kalemba and Kunicka, 2003; Faleiro
et al., 2003).
Khaki et al. (2011) investigated the role
of O. basilicum extracts as a source of natural antioxidants to assist
the sperm parameters in rats. The results of their work showed that O. basilicum
extracts significantly affect the process of spermatogenesis and might be a
promising treatment for enhancing healthy sperm parameters in rats.
The purpose of this study was to evaluate the Saudi Ocimum basilicum
leaf extract as antimicrobial agents against some human pathogens.
MATERIALS AND METHODS
Ocimum basilicum were cultivated and collected at the flowering stage
from a home garden in the Eastern Province of Saudi Arabia. In this study, extracts
from the leafs of Ocimum basilicum were tested for their antimicrobial
Preparation of extracts: Plant materials were dried in shade at room
temperature and ground by using a blender. Two hundred and fifty gram of plant
powder was soaked in 1.25-1.5 L of 95% ethanol for 5 days at room temperature.
The mixture was mixed daily for regular infusion. After a five-day period, the
extract was filtered by using Whatman filter paper No. 1. The filtrate was dried
by using a rotary evaporator at 60°C. The dried extract was stored in sterile
glass bottles at -20°C until use (Kandil et al.,
Microorganisms: Two bacterial species, gram-positive Staphylococcus
aureus and Gram-negative E. coli were used. These microorganisms
were obtained from KFUPM clinic. We also tested E. coli-ATCC 25922 and
Staphylococcus aureus-ATCC 33591 as standard strains.
Screening of antimicrobial activities: Inoculums containing 106
bacterial cells mL-1 were spread on nutrient agar medium. Antimicrobial
activity test was carried out by using the hole-plate diffusion method (Khalil
et al., 2009). Holes were made on the media by using 8 mm cork borer.
The dried plant extracts were dissolved in dimethylsulfoxide (DMSO) to a final
extract amount of 200, 150, 100 and 50 mg mL-1. Each hole (diameter
8 mm) was filled with 50 μL of plant extract. The inoculated agar plates
were incubated at 37°C for 24 h. After the incubation period, the diameter
of inhibition zone to each hole was measured in mm (the inhibition zone is an
average of 3 experiments). The inhibition zone is the area surrounding the hole
and there is no growth of the inoculated microorganism. Negative controls of
DMSO and 96% ethanol showed no antimicrobial activity against any of the tested
Negative controls were prepared using the same solvents employed to dissolve
the plant extracts. Penicillin-G (10 μg disk-1) was used as
a positive reference standard to determine the sensitivity of one strain from
each bacterial species. Antimicrobial activity was evaluated by measuring the
zone of inhibition against the test organisms. Each assay in this experiment
was repeated twice.
RESULTS AND DISCUSSION
The antimicrobial activity of ethanol leaf extracts of Ocimum basilicum
from Saudi Arabia was investigated against some human pathogenic bacteria (Staphylococcus
aureus and Escherichia coli). The strongest inhibition activity of
the leaf extract was observed against E. coli followed by Staphylococcus
aureus. Physical properties of the extract were investigated.
Physical properties: Table 1 summarizes the physical
properties of the Ocimum basilicum extract; the colour of the extract
is greenish, has intense scent, density is 0.937 g cm-3 at 25°C,
refractive index is 1.489 and specific gravity is 0.887. These physical properties
are in agreement with the physical properties reported in a previous study done
by Hanif et al. (2011).
Antimicrobial activity: The antimicrobial activity of Ocimum basilicum
leaf extract was tested against 2 pathogenic bacteria (Staphylococcus aureus
and E. coli) shown in Table 2. The tested extract
showed very strong antimicrobial activity against these 2 pathogenic bacteria.
The antimicrobial activity was evaluated by measuring the zone of inhibition.
The strongest inhibition activity of the leaf extract was observed against
E. coli (21 mm zone) at 200 mg mL-1 of leaf extract followed
by Staphylococcus aureus which showed 16 mm inhibition zone at 200 mg
mL-1 of leaf extract (Table 2). The results showed
that ethanol extract of O. basilicum has an antimicrobial effect against
E. coli (Gram negative bacteria) and Staphylococcus areous (Gram
positive bacteria) strains.
|| Physical properties of leaf extract of Ocimum basilicum
||Antimicrobial activity of Ocimum basilicum leaf extracts
against E. coli and Staphylococcus areus
|| Inhibitory effects of ethanol leaf extract of Ocimum basilicum
against (a) E. coli and compare to (b) Control
||Antimicrobial activity of the positive control penicillin-G
(10 μg disk-1)
Based on these results, the ethanol extract has a stronger and broader spectrum
of antimicrobial activities compared to positive control used in this study
(Table 3) which is Penicillin-G (10 μg disk-1).
Figure 1 shows the inhibitory effects of ethanol leaf extract
of Ocimum basilicum against E. coli compare to the control (without
extract). The inhibitory effects of ethanol leaf extract of Ocimum basilicum
against Staphylococcus areous compare to the control was shown in Fig.
2. Similar results against E. coli and Staphylococcus aureus
were obtained in a study done by Adebolu and Oladimeji (2005).
|| Inhibitory effects of ethanol leaf extract of Ocimum basilicum
against (a) Staphylococcus areous and compare to (b) Control
The strong inhibitory activities against these microorganisms showed that Ocimum
basilicum can be used as a natural agent against some human pathogens. Many
previous studies (Wannissorn et al., 2005; Bozin
et al., 2006; Lopez et al., 2005;
Sokovic et al., 2006) have reported the antimicrobial
activities of Ocimum basilicum against various microbes.
The results of the present study suggest that Ocimum basilicum extracts
possess compounds with potent antimicrobial properties against E. coli
and Staphylococcus aureusas human pathogens.
The Author would like to thank King Fahd University of Petroleum and Minerals
for their support to complete this work.
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