Antimicrobial Activity of Senna spectabilis and S. tora
Crude ethanol and aqueous extracts derived from different parts (i.e., leaf, flower, stem and pod) of Senna spectabilis and S. tora were tested in vitro against Escherichia coli, Bacillus cereus, Candida albicans and Saccharomyces cerevisiae. It was shown that only crude water extracts of S. spectabilis could inhibit the growth of B. cereus (20-25 mm, diameter of the clear zone). In contrast, both crude ethanol and aqueous extracts of S. tora were active against E. coli growth (6-10 mm) and only crude water extracts of S. tora were able to inhibit the S. cerevisiae growth. However, none of these crude extracts could inhibit the growth of C. albicans.
Since ancient time, plant and animal products have been used for treatment
of diseases and disorders. Plants in particular have been used to treat infectious
diseases due to its antimicrobial properties. This is due to the presence of
various kinds of phytochemicals including phenolic compounds, alkaloids, terpenoids
and essential oils (Lewis and Elvin-Lewis, 1995; Cowan,
1999). Therefore, plant natural products are anticipated to be an alternative
source of novel antimicrobial agent finding.
The Genus Senna (previously described as Cassia) is a pantropical
shrub of the family Leguminosae comprising of more than 300 species (Randell
and Barlow, 1998). It is widely distributed in the tropical countries such
as the USA, India, Thailand, Malaysia, Indonesia and the Australasia region.
Traditionally, the sap or the extract of the plant (i.e., root, stem and sicklepod)
has been used against ringworm, ulcers and other skin diseases (Seaforth,
1962; Kirtikar and Basu, 1975). Several reports have
shown that some Senna species exhibit antimicrobial activity. S.
alata in particular is of great interest due to its broad spectrum on
pathogenic microbes (Ibrahim and Osman, 1995; Khan
et al., 2001; Somchit et al., 2003;
Phongpaichit et al., 2004). Antifungal activity
of the extracts derived from S. fistula and S. tora
has also been described (Phongpaichit et al., 2004).
In addition, an antimicrobial alkaloid derived from S. racemosa
known as cassine is also found to inhibit the growth of Staphylococcus
aureus and Bacillus subtilis (Sansores-Peraza
et al., 2000).
S. spectabilis (Thai name: Kee Lek American) and S. tora
(Thai name: Chum Hed Thai) are widely present throughout Thailand as ornamental
plants. In traditional medicine, both plant species are used to cure ringworm
and skin diseases (Farnsworth and Bunyapraphatsara, 1992).
There is not much work however regarding the antimicrobial property of these
two plants. Therefore, the aim of the present study was to evaluate the antimicrobial
potentiality of the leaf, flower, stem and pod extracts of S. spectabilis
and S. tora against the growth of some pathogenic microbes.
Materials and Methods
Plant Materials and Extraction
S. spectabilis and S. tora were collected from Tasud,
Chiang Rai, Thailand during October-November 2004 and the leaves, stem, flowers
and pods were separated individually. The plant samples were authenticated by
Mrs. Tovaranonte, the botanist of the School of Science, Mae Fah Luang University,
Thailand. Parts of S. spectabilis and S. tora were
oven dried at 45°C for 24-48 h and macerated into powder form. Extraction
using Soxhlet apparatus with either 95% (v/v) ethanol or distilled water for
24 h was carried out. The resultant extraction was freeze dried for 24-48 h
and kept at 4°C until use. In addition, to compare the results of extracting
procedure, the grounded samples were also extracted with either 95% ethanol
for 48 h or with boiling water for 1 h at room temperature. After filtrating,
fractions were evaporated to dryness, freeze-dried and stored in the refrigerator
Microorganisms and Media
The microorganisms used in this study were bacteria (Escherichia coli
TISTR780 and Bacillus cereus TISTR687) and yeasts (Saccharomyces cerevisiae
TISTR5049 and Candida albicans TISTR5239). All microorganisms were obtained
from the Microbiological Resources Centre (MIRCEN), Thailand Institute of Scientific
and Technological Research, Thailand. For routine culture and maintenance, tryptic
soy agar (Difco) and Yeast and Mould agar (Difco) were used for bacteria and
Antimicrobial Activity Test
In this study, agar disc diffusion method was performed to determine antimicrobial
activity of the crude extracts (Collins et al., 2004).
Initially, microbial strains were grown in appropriate media to exponential
phase (between 18-24 h). The microbial cell suspensions used as inoculum were
then prepared in the range of 106-108 cells per plate.
Sterile 6.0 mm diameter blank disc were impregnated into the crude extracts
at the concentration of 75 mg mL-1, placed on the agar and incubated
either at 37°C for 24 h for bacteria or 30°C for 24-48 h for yeasts.
Impregnated disc with distilled water and 10% ethanol were used as control.
Antimicrobial activities were indicated by clear zones of growth inhibition.
Minimum inhibitory concentrations (MIC) was also determined using different
dilutions of the extracts as follows: 0, 10, 25, 30, 40, 50 and 70 mg mL-1.
The lowest concentration which did not show any growth of the tested microorganism
was interpreted as the MIC.
Results and Discussion
Traditional use of plants in the Genus Senna is often related to treatment of superficial fungal infection. The present study was further explored if the Senna plants could be used against other microbial groups. For this, crude extracts of S. spectabilis and S. tora were prepared from different parts (i.e., flower and leave) using two solvents: water and ethanol. In addition, heat treatment during the extracting procedure was also considered whether this could affect the antimicrobial activity of the crude extracts prepared. For initial screening, 75 mg mL-1 of crude extracts were used and results of the antimicrobial activity tests of S. spectabilis and S. tora are shown in Table 1 and 2, respectively.
It was found that, for S. spectabilis, only crude water extracts
had an inhibitory effect on B. cereus growth. The anti-Bacillus
activity was found in both flower and leave samples. Although high temperature
(by Soxhlet method) seems not to affect the activity of the active compound(s)
in the flower parts, this terminates the inhibitory effect of the compound(s)
in the leaves. For S. tora, crude extracts derived from pods,
leaves and stems were able to inhibit the growth of E. coli and
S. cerevisiae in which the results were varied depending on the
solvents used and the extracting methods.
|| Antimicrobial activity of flower and leaf extracts of S.
|aF, Flowers; L, Leaves, bA1 and A2,
aqueous extracts by Soxhlet and non-Soxhlet method; E1 and E2, ethanol extracts
by Soxhlet and non-Soxhlet preparation
|| In vitro antimicrobial activity of S. tora
|aP, Pods; L, Leaves; S, Stems, bA1 and
A2, aqueous extracts by Soxhlet and non-Soxhlet method; E1 and E2, ethanol
extracts by Soxhlet and non-Soxhlet preparation
||Minimum inhibitory concentrations (MICs) of the aqueous extracts
of S. spectabilis. The antimicrobial test was performed against
|aFA1 and FA2, crude extracts from flowers by Soxhlet
and non-Soxhlet methods; LA2, crude extracts from leaves by non-Soxhlet
preparation, Data shown are mean of diameter of inhibition zones±SD
It should also be noted that none of these crude extracts (from both S.
spectabilis and S. tora) could inhibit the growth of opportunistic
fungal pathogen C. albicans. Due to high inhibition zone of
S. spectabilis water crude extracts on the food-borne pathogen
B. cereus, further experiment was performed to determine the MIC.
It was found that the MIC of the extracts from both flower and leave samples
was 30 mg mL-1 (Table 3).
This present study further describes antibacterial property of S. spectabilis and S. tora. Especially for S. spectabilis, its aqueous extracts seem to be effective against the food-borne pathogen B. cereus (inhibition zones of 20-25 mm diameter). In contrast, both aqueous and ethanol extracts of S. tora, albeit ineffective, show inhibitory effect on E. coli. Future studies with purified active compounds may be useful to evaluate the actual antibacterial properties of these plants. In addition, toxicological experiment must also be undertaken to ensure the safe use.
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