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Antimicrobial assay of Stevia Rebaudiana Bertoni leaf extracts against 10 pathogens

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With an objective of understanding the antimicrobial potential of Stevia rebaudiana (popularly called as Stevia and synonymously known as ‘sugar substitute’ belongs to family Asteraceae), chemical extracts from its leaves were subjected to microbial assay using six solvents against ten selected pathogenic as well as food spoiling fungal (Alternaria solani, Helminthosporium solani, Aspergillus niger, Penicillium chrysogenum) and pathogenic bacterial (Escherichia coli, Bacillus subtilis, Enterococcus faecalis, Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus) isolates. 250μg/ml of petroleum ether extract (minimum inhibitory concentration) was found sufficient enough to inhibit the growth of test microorganism E.coli completely in petriplates (by plate dilution method). S. aureus amongst bacteria and P. chrysogenum amongst fungi exhibited highest range of susceptibility against four extracts namely; water, petroleum ether, cyclo-hexane, and chloroform but B. subtilis was found to have highest resistance to all except petroleum ether and acetone extract. Highest antifungal index (AfI-15mm) and antibacterial index (AbI-11.2mm) was obtained for petroleum ether extract against all pathogens signifying its best antimicrobial potentiality but ethanol and cyclo-hexane extracts were proved to be least effective (lowest AbI and AfI). Invariably cyclo-hexane, acetone and ethanol did not show anti fungal activity except demonstrating selective inhibition to specific microorganisms P. chrysogenum 8.0mm), A. solani (7.0mm) and A. niger (9.0mm) respectively. The above findings support the idea that plant extracts of Stevia rebaudiana Bertoni leaves may have a role to be used as pharmaceuticals and/or preservatives.
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Antimicrobial assay of Stevia rebaudiana Bertoni
Regular International Journal of Integrative Biology
A journal for biology beyond borders
ISSN 0973-8363
Antimicrobial assay of Stevia rebaudiana Bertoni leaf extracts
against 10 pathogens
Sumit Ghosh, Enketeswara Subudhi *, Sanghamitra Nayak
Center of Biotechnology, Siksha ‘o’ Anusandhan University, Bhubaneswar, India
Submitted: 2 Jan. 2008; Accepted: 18 Feb. 2008
Abstract
With an objective of understanding the antimicrobial potential of Stevia rebaudiana (popularly called as Stevia
and synonymously known as ‘sugar substitute’ belongs to family Asteraceae), chemical extracts from its leaves
were subjected to microbial assay using six solvents against ten selected pathogenic as well as food spoiling
fungal (Alternaria solani, Helminthosporium solani, Aspergillus niger, Penicillium chrysogenum) and
pathogenic bacterial (Escherichia coli, Bacillus subtilis, Enterococcus faecalis, Proteus mirabilis, Pseudomonas
aeruginosa, Staphylococcus aureus) isolates. 250μg/ml of petroleum ether extract (minimum inhibitory
concentration) was found sufficient enough to inhibit the growth of test microorganism E.coli completely in
petriplates (by plate dilution method). S. aureus amongst bacteria and P. chrysogenum amongst fungi exhibited
highest range of susceptibility against four extracts namely; water, petroleum ether, cyclo-hexane, and
chloroform but B. subtilis was found to have highest resistance to all except petroleum ether and acetone extract.
Highest antifungal index (AfI-15mm) and antibacterial index (AbI-11.2mm) was obtained for petroleum ether
extract against all pathogens signifying its best antimicrobial potentiality but ethanol and cyclo-hexane extracts
were proved to be least effective (lowest AbI and AfI). Invariably cyclo-hexane, acetone and ethanol did not
show anti fungal activity except demonstrating selective inhibition to specific microorganisms P. chrysogenum
8.0mm), A. solani (7.0mm) and A. niger (9.0mm) respectively. The above findings support the idea that plant
extracts of Stevia rebaudiana Bertoni leaves may have a role to be used as pharmaceuticals and/or preservatives.
Keywords: Stevia rebaudiana Bertoni, Antimicrobial property, Plant extracts, Anti bacterial Index, Anti fungal
index.
INTRODUCTION INTRODUCTION
Stevia rebaudiana, a natural alternative to
artificial sweetener found to contain over 100
phytochemicals including well characterized
stevioside and rebaudioside A (Komissarenko et
al., 1994). Besides, it is well known for its
application in treatment of many diseases like
diabetes, candidacies, high blood pressure and
weight loss in various traditional systems of
medicine. In recent times, the extract has been
subjected to rigorous chemical, bio-chemical,
pharmacological, clinical and toxicological
investigations and many new therapeutic
applications have been emerged out (Pinheiro,
1987; and Takahashi, 2001). Thus with time
traditional uses have been rationalized on the
basis of modern scientific approaches. In
addition, there has been a great interest in
exploration and use of natural antimicrobial
compounds of plant origin to treat diseases
because of development of resistance by
pathogens, expensive treatment regimen of
synthetic drugs already in practice and their
gross side effects due to indiscriminate use
(Nychas, 1995; Tauxe, 1997; Cowan, 1999;
Smid and Gorris, 1999; Sharif, 2001; Tomoko et
al., 2002). Microbiological investigation of
stevia plant extract against pathogenic species
using an array of solvents has neither been
attempted earlier by many workers seriously nor
reported much (Takaki, 1985; Tomita, 1997;
Tadhani et al., 2006). Therefore, efforts are taken
in this present investigation on antimicrobial
Stevia rebaudiana, a natural alternative to
artificial sweetener found to contain over 100
phytochemicals including well characterized
stevioside and rebaudioside A (Komissarenko et
al., 1994). Besides, it is well known for its
application in treatment of many diseases like
diabetes, candidacies, high blood pressure and
weight loss in various traditional systems of
medicine. In recent times, the extract has been
subjected to rigorous chemical, bio-chemical,
pharmacological, clinical and toxicological
investigations and many new therapeutic
applications have been emerged out (Pinheiro,
1987; and Takahashi, 2001). Thus with time
traditional uses have been rationalized on the
basis of modern scientific approaches. In
addition, there has been a great interest in
exploration and use of natural antimicrobial
compounds of plant origin to treat diseases
because of development of resistance by
pathogens, expensive treatment regimen of
synthetic drugs already in practice and their
gross side effects due to indiscriminate use
(Nychas, 1995; Tauxe, 1997; Cowan, 1999;
Smid and Gorris, 1999; Sharif, 2001; Tomoko et
al., 2002). Microbiological investigation of
stevia plant extract against pathogenic species
using an array of solvents has neither been
attempted earlier by many workers seriously nor
reported much (Takaki, 1985; Tomita, 1997;
Tadhani et al., 2006). Therefore, efforts are taken
in this present investigation on antimicrobial
*Corresponding author:
Enketeswara Subudhi, Ph.D.
Center of Biotechnology,
Siksha ‘o’ Anusandhan University, Jagamara,
Bhubaneswar- 751030, India
Email: esubudhi2005@yahoo.com
International Journal of Integrative Biology IJIB, 2008, Vol. 2, No. 1, 27
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Antimicrobial assay of Stevia rebaudiana Bertoni
assay of a range of six solvents by using Stevia
rebaudiana leaves against a host of 10 selected
disease causing and food spoiling test organisms.
The present work exclusively deals with a
greater scope of analysis using four more
solvents; acetone, chloroform, cyclohexane and
petroleum ether which was not being undertaken
by earlier workers.
MATERIALS AND METHODS
Plant Materials and Microorganisms
Fresh leaves collected from the young plantlets
grown in Silviculture station of Department of
Forest, Orissa were packed in polythene bags
and stored at -18ºC until its use.
Six bacterial (Escherichia coli MTCC1089,
Bacillus subtilis MTCC 441, Enterococcus
faecalis MTCC 2729, Proteus mirabilis MTCC
3310, Pseudomonas aeruginosa MTCC 647,
Staphylococcus aureus MTCC3160) and four
fungal (Alternaria solani MTCC 2101,
Aspergillus niger MTCC 1344,
Helminthosporium solani MTCC 2075,
Penicillium chrysogenum MTCC 161) isolates
obtained from Microbial type culture collection
& gene bank (MTCC), Chandigarh, India were
stored at -20ºC. These microorganisms were
selected for microbial assay study as these are
common pathogens either to plants or animals or
cause food spoilage. The pure cultures were
maintained by routine sub-culturing at one week
interval in nutrient agar and potato dextrose agar
slants for bacteria and fungi respectively (Hi-
Media laboratories private limited, Mumbai,
India).
Preparation of extracts
Stevia rebaudiana (popularly called as Stevia
and synonymously known as ‘sugar substitute’
belongs to family Asteraceae) leaves were
washed, air dried for 7-8 days, grinded into
powder and 100 g weighed powder was taken for
extraction in the flask of Soxhelet apparatus
using six different solvents viz; water, ethanol,
petroleum ether, cyclo-hexane, acetone and
chloroform (all solvents used were HPLC grade)
separately at temperature 20ºC for 3-4 hours
except in case of chloroform extraction where
the leaf sample was submerged in 10%
chloroform for 2-3 days at room temperature.
The extracts were filtered using Whatman No.1
filter paper and the filtrates were then evaporated
to dryness under reduced pressure. The residual
yield of water, ethanol, petroleum ether, cyclo-
hexane, acetone and chloroform extracts were
found to be 50 g %, 30 g %, 10 g %, 25 g %, 20
g % and 20 g % respectively. The extracts were
stored in labeled sterile screw capped bottles at -
20 ºC until further analysis.
Determination of minimum inhibitory
concentration (MIC)
Plate dilution method was followed to determine
MIC of petroleum ether extract taking different
concentrations (100, 250, 500,750μg/ml) against
0.1 ml of 10-4 inoculum dilution prepared form
24 hours incubated culture of E.coli into a sterile
petriplate followed by pouring of 20ml
autoclaved nutrient agar media so as to
understand the minimum concentration needed to
prevent the growth of the microbial strain and
use the obtained MIC from this test for
evaluation of inhibition zone diameter for all
other extracts against ten test microorganisms.
The seeded plates were incubated at 37ºC for 48
hours and the growth was noted down for
different volumes of extract separately. All the
experiments were done in triplicates and positive,
negatives controls were run parallel along with
sample analysis. The main objective of the
present work being comparative evaluation of
anti microbial potential of several extracts along
with standard antibiotics by measuring diameter
of inhibition zone (Janssen et al., 1986, Baratta
et al., 1998), MIC was obtained for one extract
using E. coli.
Antimicrobial Assay
All extracts were subjected to antimicrobial
assay by measuring the diameter of zone of
inhibition (IZD) using disc diffusion technique.
Nutrient agar and potato dextrose agar plates
were prepared by pouring 20ml each in sterile
Petri dishes for bacterial and fungal assay
respectively and allowed to solidify. 0.2 ml of
10-4 dilution of 24 hours old bacterial and 48
hours old fungal cultures were used so as to
ensure the concentration of these organisms to
contain approximately 1X 106 CFU/ml. Sterilized
cotton swabs dipped in respective cultures were
swabbed on solidified agar surface. Pre-sterilized
filter paper discs of 5mm diameter which absorbs
10-12μg sample/disc were dipped into individual
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Antimicrobial assay of Stevia rebaudiana Bertoni
extract of 250μg/ml concentration separately and
placed on the swabbed agar plates before
incubation. Similar process is followed for
controls using streptomycin and cotrimazole
discs (10μg drug/disc), obtained from Hi-Media
laboratories private limited, Mumbai, India as
standard against bacteria and fungi respectively.
At the end of incubation period diameter of
inhibition zones formed in all three replicates
were measured in mm using measuring scale and
the average of the three was determined (Barry et
al., 1985).
Antimicrobial Activity Index
Antibacterial index (AbI) and antifungal index
(AfI) for individual chemical extract of stevia
were calculated as the mean value of zone of
inhibition obtained against all individual
bacterial and fungal test strains respectively
(Saikia et al., 2001).
Statistical Analysis
Antimicrobial activity evaluated in terms of IZD
was compared statistically (ANOVA) to
understand the level of significance between two
treatments, the most potent extract showing
highest activity and one of the least potent
extracts in terms of F-values using statistical
package PAST.
RESULTS AND DISCUSSION
A concentration of 250μg/ml of petroleum ether
extract was found sufficient enough to inhibit the
growth of test microorganism E.coli completely
in Petri plates. This indicates better effectiveness
of the extract at lower concentration level
preventing the growth of microorganisms.
It is clearly depicted in table 1 that among the
bacterial pathogens selected for this study,
highest rate of susceptibility was exhibited by S.
aureus invariably by all four extracts petroleum
ether (16.3mm), cyclohexane (9.0mm),
chloroform (11.0mm), water extracts (9.3mm)
except acetone (5.0mm) and ethanol (5.0mm)
which were not able to inhibit this specific
microorganism at all. P. aeruginosa and P.
mirabilis showed highest resistance to different
extracts except against petroleum ether (showing
IZD 11mm, 10mm) and ethanol (8mm, 10.8mm).
Among fungal strains used higher susceptibility
was observed by P. chrysogenum, A. niger and
least susceptible fungus was found to be A.
solani against the extracts in general.
Of all the extracts petroleum ether has highest
AbI with highest antimicrobial activity against 3
bacterial species S. aureus, E. faecalis, P.
aeruginosa forming an IZD of 16.3mm, 13mm,
11mm respectively. The AbI indicates petroleum
ether has got the total best antimicrobial property
against all six bacterial species. Against other
three bacterial species E.coli, P. mirabilis, B.
subtilis, the best activity was shown by water,
ethanol and acetone extract with an IZD of
11mm, 10.6mm and 10.3mm respectively. The
water extract has got the antimicrobial activity
only against E. coli, S. aureus and B subtilis.
Similar results were reported by M.B. Tadhani
and R. Subhash (2006) that water extract of
Stevia leaf showed activity against B. subtilis
and S. aureus only. IZD obtained by the ethanol
extract in the present study also coincides with
the response got by same workers using
methanol extract which gave the highest zone of
inhibition against P. aeruginosa and minimum
against S. aureus and yeast. Smaller anti
bacterial index as shown in the table indicates
less activity as observed by few extracts like
acetone against E.coli, B. subtilis, by ethanol
against P. mirabilis, by chloroform against S.
aureus, by cyclohexane against S. aureus and by
ehanol against P. mirabilis when compared to
standard antibiotics (AbI 22.2). No activity was
found in few extracts of stevia against selected
pathogens which are represented as 5.0 mm IZD
in the table.1.
The highest anti fungal index was found in case
of petroleum ether extract (AfI 15) irrespective of
fungal species used, showing the highest activity
forming (IZD of 16mm,14mm,16mm,14mm)
followed by water extract (8.75 AfI) with IZD of
(11mm, 10mm, 6mm, 8mm) against those
fungal species namely A. niger, P. chrysogenum,
A. solani, H. solani as depicted in table 1. Very
less activity was observed by ethanol, acetone,
chloroform and cyclohexane extracts of AfI
5,5.5,5.75 and 6.5 respectively except some
specific activity against organisms like H. solani
(9.0mm), A. niger (9.0mm), A. solani (7.0mm),
P. chrysogenum (8.0mm).
It can be concluded that the calculated F-value
(22.33) between IZD obtained form the treatment
of petroleum ether extract showing the highest
antimicrobial activity and cyclohexane, one of
the least potent extract was found to be greater
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Antimicrobial assay of Stevia rebaudiana Bertoni
TABLE 1: Antifungal and Antibacterial Activity of Solvent Extracts Of Stevia (IZD in mm)
Extract
Microorganism
Petrolium
ether
Cyclo
hexane
Chloroform
Water
Acetone
Ethanol
Standard
A.niger
16 5 5 11 5 9 23
P. chrysogenum
14 8 7 10 5 5 22
A. solani
16 5 5 6 7 5 11
H. solani
14 5 9 8 5 5 10
Antifungal index
(AfI) 15 5.75 6.5 8.75 5.5 5 16.5
E. coli
7 5 7 11 10 5 22
P.aeruginosa
11 7 5 5 6 8 25
P. mirabilis
10 5 7 5 5 10.6 23
E. faecalis
13 6 5 5 8.3 5 18
S. aureus
16.3 9 11 9.3 5 5 23
B subtilis
10 5 5 9 10.3 5 22.5
Antibacterial index
(AbI) 11.2 6.1 6.6 7.4 7.4 6.4 22.2
than the tabulated F-value (4.8) with P 0.001
(for degrees of freedom n1=5 and n2=54). Thus
the deviation due to different treatments of
petroleum ether and cyclohexane was found to
be highly significant.
The present investigations endow with the basic
information about new non antibiotic drug
molecules of plant origin, especially petroleum
ether extract of stevia leaves which is found to be
potent enough in exhibiting substantial
antimicrobial activity against dreaded animal
pathogens like S. aureus, E. faecalis bacteria.
Possession of sizeable antimicrobial activity
against food spoiling fungi like A. niger, P.
chrysogenum and bacteria S. aureus may be
explored for a value addition as natural food
preservative to sugar substituting property of
stevia used now a days for diet restricted
package food products. Extraordinary anti fungal
activity higher than the standard fungicide used
against plant pathogens H. solani and A. solani
may be substituted as potent bio-fungicide.
Therefore, these molecules could be proved as
future potential candidates either as non
antibiotic pharmaceuticals or food preservatives
and/or plant micro-biocides after proper toxicity
study in plant and animal models and clinical
trials are addressed.
Acknowledgement
Authors are grateful to Dr. S. C. Si, Dean, Center of
Biotechnology and Dr M. Nayak, President, Siksha
‘O’ Anusandhan University, Bhubaneswar for
providing the necessary facilities to carry out above
work.
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... S Jayaraman et al., [46] Performed the Antimicrobial activity of solvent (methanol, ethanol) Extract of leaf of Stevia rebaudiana by using Agar-well diffusion methods in albino rats, It was found that solvent Extract of Stevia rebaudiana leaf showed significant antibacterial activity, the zone of inhibition was found to be in acetone extract: S. aureus = 19 mm., Bacillus subtulis = 18 mm and Ethyl acetate extract very effective against Vibrio cholera = 18 mm. Ghosh S. et al., (2008)Performed the Antimicrobial activity of solvent (methanol, ethanol) Extract of leaf of Stevia rebaudiana by using Plate dilution methods for MIC and Diffusion method for Zone of Inhibition in albeno rats, it was found that solvent Extract of Stevia rebaudiana leaf showed significant antibacterial activity, the zone of inhibition was found to be in Petroleum ether extract: have highest AbI against S. aureus, E. faecalisP. aeruginosa IZD as 16.3 mm, 13 mm, 11 mm and ethanolic, water and acetone extract the IZD= 11 mm, 10.6 mm, 10.3 mm [47]. ...
... Ghosh S. et al., (2008)Performed the Antimicrobial activity of solvent (methanol, ethanol) Extract of leaf of Stevia rebaudiana by using Plate dilution methods for MIC and Diffusion method for Zone of Inhibition in albeno rats, it was found that solvent Extract of Stevia rebaudiana leaf showed significant antibacterial activity, the zone of inhibition was found to be in Petroleum ether extract: have highest AbI against S. aureus, E. faecalisP. aeruginosa IZD as 16.3 mm, 13 mm, 11 mm and ethanolic, water and acetone extract the IZD= 11 mm, 10.6 mm, 10.3 mm [47]. Cosmetic Formulation: K Das et al., (2009)Performed the skin moisturizing activity of aqueous leaf extract of Stevia rebaudiana by using Physiological Measurement in comparison with a control placebo gel, it was found that aqueous extract of Stevia rebaudiana leaf showed significant moisturizing activity [48]. ...
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