Biokemistri, Vol. 18, No. 1, June, 2006, pp. 39-44
Phytochemical
screening and antimicrobial assessment of Abutilon mauritianum,
Bacopa monnifera and Datura stramonium
Aderotimi
BANSO 1* and SamuelADEYEMO2
1Department
of Science Laboratory Technology, The Federal Polytechnic, P.M.B. 55, Bida, Niger
State, Nigeria.
2Department of Biological Sciences, BowenUniversity, Iwo, Nigeria
*To
whom correspondence should be addressed. Tel: 08060775952, 08045028829
Received January 25, 2006
Code Number: bk06007
Abstract
Three medicinal
plants - Abutilon mauritianum, Bacopa monnifera and Datura
stramonium were assessed for phytochemical components and antimicrobial
activity. The results revealed that all the three plant extracts contained
saponins, tannins and alkaloids. Only Datura stramonium contained
glycosides. The plants exert varying inhibitory effects on Pseudomonas
aeruginosa, Klebsiella pneumonia and Escherichia coli. The minimum
inhibitory concentration of the plant extracts ranged between 10% (w/v) (Bacopa
monnifera) and 25% (w/v) (A. mauritianum and D. stramonium).
Extracts of Abutilon mauritianum, Bacopa monnifera and Datura
stramonium could be potential sources of chemotherapeutic agents.
Keywords: Phytochemical, antimicrobial, chemotherapeutic agent.
INTRODUCTION
Plants
are rich in a variety of secondary metabolites such as tannins, terpenoids,
alkaloids, flavonoids, phenols, steroids, glycosides and volatile oils1.
It is necessary to identify the phytochemical components of local medicinal
plants usually employed by herbalists in the treatment of diseases, especially
now that there are proposals on the integration of traditional medicine in
health care programme in Nigeria. In addition, investigations into antimicrobial
activities of local medicinal plants will expose the plants as potential
sources of therapeutic agents2. The volatile oils of black pepper (Piper
nigrum L.) were assessed for antibacterial activity3. The stem
bark extracts of Enantia chloranta showed antimicrobial activity against
some bacteria4. The antibacterial and antifungal activities of Zanthoxylum
budrungia has been reported5.
The use of chemotherapeutic agents in the treatment of
infectious diseases has been known from time immemorial. The ancient man
discovered the therapeutic value of some herbs by trial and error6.
The alternative use of folkloric medicinal plants detailed their alternative
use in medicine in Jamaican society has been studied7. The effective
inhibition of the growth of some Grampositive and Gramnegative bacteria by
the chloroform and ethyl acetate extracts of Nyctanthes arbortritis
fresh flowers has been reported8.
Datura stramonium is an erect branched undershrub with long white flowers and spiny
spherical fruits9. Abutilon mauritianum and Bacopa
monnifera are erect branched plants. The leaves of abutilon mauritianum is
prescribed for diarrhoea gonorroea and bronchitis. The decoction of Bacopa
monnifera is given as a febrifuge and cardiac tonic10.
The aims of this study are to identify the
phytochemical components of Abutilon mauritianum (African Mallow), Bacopa
monnifera (Thyme) and Datura stramonium (Stink weed) and to
determine the antimicrobial effects of the plants extracts on Psedomonas
aeruginosa, klebsiella pneumonia and Escherichia coli. Pseudomonas
aeruginosa attaches to and colonises the mucous membranes or skin,
invades locally and produces systemic diseases19. The bacterium is
resistant to many antimicrobial agents. K. pneumoniae causes chest,
urinary and wound infections. E. coli is the most common causes of
urinary tract infection19.
MATERIALS AND METHODS
Plants
Materials and Microorganisms
The representative microorganisms used were Pseudomonas
aeruginosa, Klebsiella pneumonia and Escherichia coli. They are
medically important. The organisms were obtained from the culture collection
centre, Department of Biological Sciences, University of Ilorin. The microorganisms were tested for purity by
culturing on nutrient agar and maintained on nutrient agar slants. Leaves of Abutilon
maritianum, Bacopa monnifera and Datura stramonium used in
this study were obtained from The Federal Polytechnic, Bida, Niger State.
Identification was carried out at the Herberium Unit of Department of
Biological Sciences, University of Ilorin, Nigeria according to the criteria stipulated by International
Committee for Botanical Nomenclature.
Preparation of leaf extract
Ethanol was very effective in extracting the active
ingredients in the plants used in this study. Hence the organic solvent
(ethanol) was used as the extracting solvent in this study. Ten grammes of
ground dry leaf samples of the three plants were soaked in 250ml of 95% ethanol
contained in three separate 500ml capacity flasks. The flasks were plugged with
cotton wool, wrapped in aluminium foil, shaken vigorously and allowed to stand
in the refrigerator for 24 hours. The extract obtained were evaporated to
dryness using a rotary evaporator and stored in refrigerator in reagent bottles11.
Each extract was tested for growth/contamination by plating them on nutrient
agar at 37°C for 24 hours. No growth was observed visually and the
extract was subsequently used to assay for antimicrobial activity using the
agar diffusion method. The percentage yield of the extract was determined using
the expression:

Phytochemical
screening of Extract
The methods described by Odebiyi and Sofowora12
were used to test for the presence of saponins, tannins, alkaloids, flavonoids
and glycosides in the test samples.
a.
Determination of saponins
Each of the plant extracts (0.5g) was separately
stirred in a test tube, foaming which persisted on warming was taken as an
evidence for the presence of saponins12.
b.
Determination of tannins
Ethanolic extract of each sample (0.5g) was separately
stirred with 10ml of distilled water and then filtered. To the filtrate was added
two drops of 5% Iron (III) Chloride (FeCl3) reagent. Blue black or
blue green colouration or precipitate was taken as an indication of the
presence of tannins12.
c.
Determination of alkaloids
Extract of each plant sample (0.5g) was separately
stirred with 1% hydrochloric acid (HCl) on a steam bath. The solution obtained
was filtered and 1ml of the filtrate was treated with two drop of Mayers
reagent. The two solutions were mixed and made up to 100ml with distilled
water. Turbidity of the extract filtrate on addition of Mayers reagent was
regarded as evidence for the presence of alkaloids in the extracts12.
d.
Determination of glycosides
Coarsely powered plant material (1g) was introduced
into two different beakers. To one of the beakers was added Sulphuric acid
(5ml) while water (5ml) was added to the other beaker. The two beakers were
heated for 3 minutes and the contents filtered into labelled test tubes. The
filtrate was made alkaline with sodium hydroxide (0.5ml) and allowed to stand
for three minutes. The presence of reddish brown precipitate in the filtrate
was taken as positive for glycosides12.
e.
Determination of flavonoids
To ethanolic extract of each piece of test plant leaf
extract was added a small piece of magnesium ribbon, this was followed by
dropwise addition of concentrated hydrochloric acid. Colours ranging from
orange to red indicated flavones, red to crimson indicated flavonols, crimson
to magenta indicated flavonones12.
Antimicrobial
Test
This was performed using the agar diffusion method of
Boakye-Yiadom13 P. aeruginosa, K. pneumonia or E. coli
was inoculated on nutrient agar plate and spread uniformly using a glass
spreader. A sterilised calibrated Pasteur pipette was used to introduce
different concentrations 5% (w/v), 10% (w/v), 15% (w/v), 20% (w/v), 25% (w/v)
and 30% (w/v) of the extracts into the wells bored onto the surface of the
culture. Control experiments with no plant extracts were set up.
The plates were allowed to stand for one hour at room
temperature to allow the diffusion of the substances to proceed before the
growth of organism commenced. The plates were finally incubated at 37°C
for 24hrs.
Determination
of minimum inhibitory concentration (MIC) of the Extracts
The plant extracts (5mg/ml, 10mg/ml, 20mg/ml, 25mg/ml
and 30mg/ml) were introduced into different test tubes, each tube was
inoculated with an overnight culture P. aeruginosa, K. pneumonia or E. coli
diluted to give a final concentration of 106 cells per ml. The tubes
were incubated at 37°C for 24 hours. The lowest concentration of the
plant extracts that did not permit any visible growth of the inoculated test
organism in broth culture was regarded as the MIC in each case14.
RESULTS AND DISCUSSION
The phytochemical analysis of the plants assayed in
this study revealed that A. mauritianum, B. monnifera and D.
stramonium contained saponins, tannins and alkaloids (Table 1).
The antimicrobial activity of leaf extract of Eugenia
uniflora was reported by Adebayo et al18. The authors
also reported that tannins, glycosides and akaloids were present and that the
ethyl acetate and methanolic leaf extracts of the plant were active against E.
coli, P. vulgaris, K. pneumonia and A. niger. All
parts of the plants were strongly intoxicant and narcotic. Leaves of the plants
were burnt and the smoke inhaled for the relief of asthma and cough10.
The decoction of the leaves of Abutilon mauritianum is prescribed for
diarrhoea, gonorrhoea inflammation, bronchitis and catarrhal condition10.
A hot poutice of Bacopa monnifera is applied in bronchitis and chest
ailments of children10.
Table 1: Phytochemical
components of leaves of plants.
Chemical constituent
|
A. mauritianum
|
B. monnifera
|
D. stramonium
|
Saponins
|
+
|
±
|
±
|
Tannins
|
+
|
±
|
+
|
Alkaloids
|
++
|
+
|
++
|
glycosides
|
-
|
-
|
±
|
Flavonoids
|
+
|
-
|
-
|
+ = Positive; ++ = Strongly positive; ± = Trace; -
= Not detected; Percentage yield
of extracts: A. mauritianum = 38%;
D. stramonium = 35%, B. monnifera
= 37%
Saponins are a special class of glycosides which have
soapy characteristics15. It has also been shown that saponins are
active antifungal agents16. This therefore supports the earlier
finding that extracts of the plants used in the present work may be useful in
the chemotherapy of mycotic infections. Tannins have been reported to prevent
the development of microorganisms by precipitating microbial protein and making
nutritional proteins unavailable for them16. Classes of alkaloids
are among the major powerful poisons known15. Apart from being
poisonous, some alkaloids have also been proved to be useful in correcting
renal disdorders17; it therefore, means that the alkaloids of A.
mauritianum, B. monnifera and D. stramonium may be a poison
that can be tried on lower or higher organisms. The secondary metabolites
identified in the plant materials used in this study could be responsible for
antimicrobial activity exhibited by these plants.