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Vol. 31, 2013, No. 2: 194202 Czech J. Food Sci.

Biological Activities of Essential Oils and Methanol Extracts

of Five OcimumSpecies against Pathogenic Bacteria

S SAHA1,2, T N DHAR2, C SENGUPTA2and P GHOSH1

1Department of Botany, Cytogenetics and Plant Biotechnology Research Unit , University

of Kalyani, Nadia, West Bengal, India, 2Department of Botany, Microbiology Research Unit ,

University of Kalyani, Nadia, West Bengal, India

Abstract

S S., D .N., S C., G P.D. (2013): Biological activities of essential oils and methanolextracts of five Ocimumspecies against pathogenic bacteria. Czech J. Food Sci., 31: 194202.

Te essential oils and methanol extracts of Ocimum basilicumL., Ocimum kilimandscharicum Guerke, Ocimum gratis-

simumL, Ocimum canumSims, and Ocimum tenuiflorumL. (green type) were examined for their potential antibacterial

activities. Te chemical composition of essential oils of Ocimumspecies was analysed by GC-MS. Te inhibitory effects

of essential oils and methanol extracts were studied on two Gram-positive (Bacil lus subtilis, Micrococcus luteus)and five

Gram-negative (Pseudomonas aerug inosa , Shigella dysenteriae, Escherichia coli, Vibrio cholera, and Shigella flexneri)

bacteria using disc-diffusion method. Minimum inhibitory concentration (MIC) was assessed by micro broth dilution

method. Te antibacterial test results showed that the essential oil s ofOcimum basilicumL., Ocimum kilimandscharicum

Guerke, and Ocimum gratissimumL. strongly inhibited the growth of all of the microorganisms studied, especially of the

Gram-negative strains, whereas other two essential oils showed moderate activities. Te result may suggest that the es-sential oils of Ocimum possess compounds with antibacterial activities, and therefore could be used as natural preservative

ingredients in food and/or pharmaceutical industries.

Keywords: antibacterial activity; essential oil; GC-MS; Ocimumspecies

Medicinal and aromatic plants (MAPs) have beenused for centuries as remedies for human diseasesbecause they contain components of therapeutic

value. It has been estimated by WHO that 80% ofthe population, the majority of this in the develop-

ing countries, still rely on plant-based medicinefor primary health care needs (WHO 1993). Forthis purpose, various strategies have been devel-oped, e.g. biological screening, isolation, as wellas clinical trials for a variety of plants .

Following the advent of modern medicine, herbalmedicine suffered a setback, but during the last twoor three decades the advances in phytochemistryand in the identification of the plant compounds,providing effective against certain chronic diseasesand emergence of multidrug resistant bacteria.

his awakening has led to a sudden demand forherbal medicine. Worldwide as well as in the de-

veloping countr ies, the most humans died due toinfectious bacter ial diseases (N 2004). hebacterial organisms including both Gram positive

and Gram negative ones are the main cause of se-vere infections in humans, because they have theability to survive in harsh conditions due to theirmultiple environmental habitats (A& H 2010). Nowadays, multiple drug resist-ance is developed due to the indiscriminate use ofcommercial antimicrobial drugs commonly usedin the treatment of infectious diseases (G etal. 2008). In addition to this problem, antibioticsare sometimes associated with adverse effectson the host including hypersensitivity, immune-

Support by the University Grant Commission (UGC), New Delhi, Govt. of India, Project No. F14-2(SC)/2007/(SA-III).

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Czech J. Food Sci. Vol. 31, 2013, No. 2: 194202

suppression, and allergic reactions (W et al.1999). On the other hand, environmental safety isa major concern in many countries, and the ap-plication of synthetic agrochemicals runs the r iskof causing unacceptable environmental damage,such as health hazards to humans, toxicity to usefulnon-targeted animals and environmental pollution.he use of natural products would be a helpful wayto reduce this risk, and also the situation requiressearching for new antimicrobial substances. hescreening of the active compounds from plantshas lead to the discovery of new medicinal drugswhich show efficient protection and treatmentroles against various diseases, including cancer(K et al. 2004; S & K 2007).herefore, there is a need to develop alternative

antimicrobial drugs from medicinal plants for thetreatment of infectious diseases.

he genus Ocimuminvolves economically themost important medicinal and aromatic herbs ,undershrubs or shrubs in the world. It belongsto the family Lamiaceae, subfamily Ocimoideae,and comprises more than 30 species distributedin tropical and subtropical regions of Asia, Africa,and Central and South America (P 1992).raditionally, the genus Ocimum is widely usedfor the treatment of various ailments including

rheumatism, paralysis, epilepsy, high fever, diar-rhea, sunstroke, influenza, gonorrhea, mentalillness, abdominal pains, colds, coughs, measles,and has also antipyretic, antihelmentic, stomatic,anti-emetic, and antimalarial effects (C etal. 1990; O-O et al. 1998; N et al.2002; E et al. 2004). It is also a sourceof aroma compounds and essential oils contain-ing biologically active constituents that possessinsecticidal (D et al. 1997), nematicidal(C et al. 1982), and fungistatic properties(R et al. 1984). he active compounds pre-

sent as volatile oil from the leaves consist mainly ofeugenol, thymol, citrol, geraniol, camphor, linalooll, and methyl cinnamate (C & S 1992;J & B 2001; M et al.2002; V & M 2003; P & V2011; S et al. 2011; V et al. 2011). heseeds contain oil composed of fatty acids andsitosterol. he roots contain sitosterol and threetriterpenes A, B, and C. Additionally, they alsocontain rosmarinic acid, thymol, methyl chavicoland, citral etc. (D et al. 1968), and vitamins

C, A, and minerals like calcium, zinc, and iron(A & V 2007), as well as

chlorophyll and many other phytonutrients. Recentinterest in Ocimumhas resulted from its inhibi-tory activity against HIV-I reverse transcriptaseand platelets aggregation induced by collagen andADP (adenosine 5'-disphosphate) (O et al.1998; Y et al. 1998). However, the anti-microbial activity of Ocimumessential oil againstmicroorganisms has been investigated by someresearchers (P et al. 1986; N etal. 1999; A & O 2005; Aet al. 2005; M et al. 2011; V etal. 2011) using different techniques and their in-

vestigations mostly covered one individual or twospecies. Unfortunately, the published data on theformer subject are difficult to compare, becausethe chemical composition of essential oils is known

to vary with the local climate, harvest period, andenvironmental conditions (V &S2000),and is also dependent on the type of solvent used inthe extraction procedure (C et al. 1989). herefore,the present study is aimed at evaluating the in vitroantibacterial activity of essential oils and methanolextracts of five species of Ocimum, namely Ocimumbasilicum L., Ocimum kilimandscharicum Guerke,Ocimum gratissimum L., Ocimum canum Sims.,and Ocimum tenuiflorum L. (green type) againstthe selected microorganisms.

MATERIAL AND METHODS:

Plant material collection .Fresh leaves of Oci-mum basilicumL., Ocimum kilimandscharicumGuerke, Ocimum gratissimumL., Ocimum ca-num Sims., and Ocimum tenuiflorum L. (greentype) were collected from medicinal and aromaticplant garden, Department of Botany, Universityof Kalyani, Kalyani, West Bengal, India , in Augustof 2011 (able 1), which is located at 2257'N lati-

tude, 8822'E longitude with an average altitude of9.75 m a.s .l. he taxonomic identification of theplant material was confirmed by Dr. G. G. Maity,axonomy and Plant systematic Unit, Departmentof Botany, University of Kalyani. he voucherspecimens (143, 148, 149, 150, and 163 KUH,respectively) were deposited and preserved atthe Department of Botany, University of Kalyani,Kalyani, and West Bengal, India, for reference.

Preparation of methanolic plant extracts . Eachcollected plant material was dried in the shade and

ground in a grinder with a 2 mm diameter mesh.he dried and powdered leaves (100 g) were succes-

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sively extracted with 500 ml of methanol (1:5 w/v)using a Soxhlet extractor for 72 h at a temperaturenot exceeding the boiling point of the solvent (Let al. 1999). he extracts were filtered using What-man filter paper (No. 1) and then concentrated in

vacuo at 40C using a rotary ev aporator (Buchi

Rotavapor R-200; Buchi Labortechnik AG, Flawil,Switzerland). he extracts were then lyophilisedand kept in the dark at +4C until tested.

Extraction of the essential oil s.he air-driedand ground aerial parts of the plants collectedwere submitted to water distillation for 2.5 h us-ing a Clevenger-type apparatus (C et al.1928)). he essential oils obtained were dried overanhydrous sodium sulphate and, after filtration,stored at +4C until tested and analysed.

GC-MS and GC-FID analysis. GC-MS analyses

of the essential oils were performed on a Hewlett-Packard gas chromatograph, model 6890, equippedwith a FID, using HP-5MS capillary column (30 mlength 0.25 mm i.d. 0.25 m film thickness) (Agi-lent echnologies, Santa Clara, USA). Te injectorwas set at 250C and the detector at 280C, respec-tively. Te oven temperature of the chromatogramwas raised from 60C to 280C, respectively, at theheating rate of 10C/min, and was then isothermallyheld for 5 minutes. Te injector volume was 1.0 l.Te solvent delay was 2 min and it was injected in asplit ratio of 1:10. Helium was used as the carrier gas

at 15 P.S.I. inlet pressure. Te essential oil constitu-ents were identified by the comparison of their GCretention indices (RI) and mass spectra with those ofthe authentic standard compounds. Quantificationof the relative amounts of the individual componentswas performed according to the area percentagemethod ( et al. 2006) for each plant.

Antibacterial activity

Test microorganism. he methanol extracts andessential oils were individually tested against a

panel of microorganisms including Gram-positiveBacillus subtilis (MCC 441),Micrococcus luteus(MCC 2522), Gram-negativePseudomonas aeru-

ginosa (MCC 741), Shigella dysenteriae (Clini-cal isolate), Escherichia coli (MCC 443), Vibriocholera(MCC 3904), and Shigella flexneri (MCC

1457). All the bacterial strains except Shigelladysenteriaewere obtained from the Institute ofMicrobial echnology, Chandigarh, India. hereference strains of bacteria were maintained onnutrient agar (HiMedia, Mumbai, India) slants at4C with a subculture period of 30 days.

Preparation of McFarland standard.Te turbid-ity standard was prepared by mixing 0.5 ml of 1.75%(w/v) BaCl

22H

2O with 99.5 ml of 1% H

2SO

4BaSO

4(v/v). Te standard was put into screw cap test tubeto compare the turbidity. Te bacterial cultures of

the selected strains were grown overnight and weresubsequently mixed with physiological saline. ur-bidity was corrected by adding sterile saline untilMcFarland 0.5 BaSO

4turbidity standard 108Colony

Forming Unit (CFU) per ml was achieved. Teseinocula were used for seeding of the nutrient agar.

Disc-diffusion assay. he essential oils and meth-anol extracts were dissolved in DMSO (dimethyl-sulfoxide) to a final concentration of 30 mg/mland sterilised through filtration using 0.45 mmembrane filters. he antibacterial tests were thencarried out by disc diffusion method (M et

al. 1995) using 100 l of the suspension containing108CFU/ml of bacteria on nutrient agar. he discs(6 mm in diameter) were impregnated with 10 lof essential oil or 30 mg/ml extracts (300 g/disc)placed on the inoculated agar. Negative controlswere prepared using DMSO. Gentamicin (10 gper disc) was used as positive reference standard todetermine the sensitivity of each bacterial speciestested. he inoculated plates were incubated at37C for 24 hours. he antibacterial activity wasevaluated by measuring the zone of inhibition,

the diameters of these zones being measured inmillimeters against the test organisms.

able 1. Plants and plant parts used

No. Scientific name Common name Family Parts used

1. Ocimum basilicumL. sweet basil

Lamiaceae dried leaves

2. Ocimum kilimandscharicumGuerke. camphor basil

3. Ocimum gratissimumL. shrubby basil

4. Ocimum canumSims. hoary basil

5. Ocimum tenuiflorumL. (green type) holy basil

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Determination of minimum inhibitory con-

centration.he minimal inhibitory concentration(MIC) values were followed with the bacteriastrains sensitive to the essential oils and/or ex-tracts in the disc diffusion assay. he inoculaof the bacterial strains were prepared from 12 hbroth cultures and the suspensions were adjustedto 0.5 McFarland standard turbidity. he essentialoils and extracts of Ocimumssp. dissolved in 10%DMSO, were first diluted to the highest concen-tration (500 g/ml) to be tested, and then serialtwofold dilutions were made in order to obtaina concentration range from 7.8 to 500 g/ml in10 ml sterile test tubes containing the nutrientbroth. MIC values of the extracts against bacterialstrains were determined based on the micro well

dilution method as previously described (Set al. 2004). he 96-well plates were prepared bydispensing into each well 95 l of the nutrient brothand 5 l of the inoculum. A volume of 100 l fromthe stock solutions ofOcimumspp. essential oilsand extracts initially prepared at the concentrationof 500 g/ml was added into the first wells. hen,100 l from their serial dilutions was transferredinto six consecutive wells. he last well containing195 l of the nutrient broth without the compoundand 5 l of the inoculum on each strip was used

as negative control. he final volume in each wellwas 200 l. he plate was covered with a sterileplate sealer and then incubated at the appropri-ate temperature 37C for 24 hours. he bacterialgrowth was determined by absorbance measured

at 600 nm using the ELx 800 universal microplatereader (Biotek Instrument Inc., Winooski, USA) andconfirmed by plating 5 l samples from clear wellson nutrient agar medium. he MIC was definedas the lowest concentration of the compound toinhibit the growth of microorganisms. Each testin this study was repeated at least twice.

RESULTS AND DISCUSSION

Essential oil composition

he percent chemical composition of the essentialoils of five species of Ocimum,namely O. basilicum,O. kilimandscharicum, O. gratissimum.O. canum,

and O. tenuiflorum(green type) is given in able2 in the order of the retention times of the con-stituents. he yields of the essential oils obtainedfrom dry leaves were 1.77, 1.92, 1.63, 1.81, and1.73% (v/w), respectively. he main constituents ofO. basilicumwere geraniol (34.89%), citral (23.51%),linalool (2.21%), and eugenol (1.33%); O. kili-mandscharicum camphor (21.65%), eugenol(9.65%), cineole (2.07%), and citral (1.23%); O. gratis-

simum eugenol (47.45%), citronellal (3.56%),cineole (1.97%), geraniol (1.52%), and vanillin

(1.52%); O. canum camphor (3.47%), cineole(1.44%), vanillin (1.03%), and O. tenuiflorum(greentype) eugenol (8.81), citronellal (1.44%), and

vani ll in (1 .16%), respec tively. he essentia l oi lcomposition of O. basilicum, O. gratissimum, and

able 2.Percentage composition of the essential oils of five species of Ocimum cultivated in West Bengal

CompoundRetention indicesa

(RI) (min)

Essential oil (%)b

O. basilicumL.O. kilimandscha-

ricumGuerkeO. gratissimumL. O. canumSims.

O. tenuiflorum L.(green type)

-Pinene 4.76 0.23 0.98 0.12 0.17

Camphor 4.87 0.64 21.65 0.15 3.47 0.05Citral 5.26 23.51 1.23 0.52 0.33 0.22

Geraniol 5.76 34.89 0.49 1.52 0.14 0.83

Cineole 5.83 0.05 2.07 1.97 1.44

-Pinene 5.92 0.19 1.02 0.18 0.13 0.09

Citronellal 5.96 0.59 0.51 3.56 0.79 1.44

Eugenol 6.57 1.33 9.65 47.45 0.32 8.81

Vanillin 6.72 0.27 0.30 1.52 1.03 1.16

Linalool 7.41 2.21 0.23 0.12 0.02

a

identification of oil components was based on their relative retention indices (retention times) with those of authenticstandards; bquantitative estimation was done by analysis of FID area percent data

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O. kilimandscharicumobtained from plants grownin northern India, was found to be rich in O. ba-

sil icummethyl chavicol and linalool (21.9%); O.grati ssimum eugenol (72.2%), 1.8-cineole (7.6%),germacrene D (2.7%) and -caryophyllene (1.7%);and O. kilimandscharicum camphor (64.9%),

limonene (8.7%), in accordance with previousreport (P & V 2011). Similar resultswere found with O. gratissimumand O. kilimand-

scharicumin sub t ropical India (V et al.2011). In the oils obtained from the aerial partof O. basilicumgrown in Colombia and Bulgaria,linalool and methyl cinnamate were reported a sthe major components of volatile oils, respec-

tively (J & B2001; V &M 2003). It is interesting that the oilsextracted from Ocimum basilicumL. collectedfrom Bangladesh contain linalool and geraniolas their main constituents (M et al.2002), and the authors concluded that the oil

composition could be dependent on the climaticconditions. he chemical composition of essentialoils of Ocimumspecies shows a large interspecies

variability and, within the same species , it seemsto depend on the genetic characteristics of theplant and on the conditions under which it hasgrown. In the present study, our findings on themajor components of O. kilimandscharicumand

able 3. Antibacterial activity of the essential oil and methanol extract of Ocimumssp. against the bacterial strains

tested based on disc diffusion method

Microorganism

Inhibition zone in diameter (mm) around the discs impregnated with 10 l of essentialoils and extracts (300 g/disc)

essential oil (10 l/disc)a MeOH extractsb gentamicin(10 g/disc)E1 E2 E3 E4 E5 M1 M2 M3 M4 M5

B. subtilis(MCC 441) 22 24 18 15 22 8 8 7 c 26

M. luteus (MCC 1541) 20 16 16 14 18 26

P. aeruginosa (MCC 741) 23 21 22 15 14 13

S. dysenteriae(clinical isolate) 16 16 15 18 18

E. coli (MCC 443) 16 17 21 9 10 8 8 30

V. cholera(MCC 3904) 22 16 21 18 18 10 7 17

S. flexneri(MCC 1457) 18 18 15 21 27

E1E5 essential oils: EI Ocimum basilicumL.; E2 Ocimum kilimandscharicumGuerke; E3 Ocimum gratissimumL.;E4 Ocimum canumSims; E5 Ocimum tenuiflorumL. (green type); M1M5 methanol extracts: M1 Ocimum basilicum

L.; M2 Ocimum kilimandscharicumGuerke; M3 Ocimum gratissimumL.; M4 Ocimum canumSims; M5 Ocimum

tenuiflorumL. (green type); not active; ainhibition zone in diameter (mm) around the discs impregnated with 10 l of

essential oil; binhibition zone in diameter (mm) around the discs impregnated with extracts (300 g/disc)

able 4.Te MIC values of essential oils of the five species of Ocimumagainst the bacterial strains tested in micro-

dilution assay (g/ml)

MicroorganismEssential oil

O. basilicumO. kilimand-

scharicumO. gratissimum O. canum

O. tenuiflorum(green type)

B. subtilis(MCC 441) 15.62 15.62 62.50 62.50 62.50

M. luteus (MCC 1541) 31.25 62.50 125 125 125

P. aeruginosa (MCC 741) 62.50 62.50 125 250 250

S. dysenteriae(clinical isolate) 125 250 250 125 nt

E. coli (MCC 443) 15.62 31.50 31.50 nt 500

V. cholera(MCC 3904) 31.25 125 125 125 250

S. flexneri(MCC 1457) 15.62 62.50 125 nt 62.50

nt not tested

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O. gratissimumoils were in agreement with theprevious report ( V et al.2011). Accordingto the literature, the major compounds concernedof O. basilicum, O. canum, and O. tenuiflorum(green type) are different. he observed differ-ences may be due to the different env ironmentaland genetic factors, different chemotypes , and thenutritional status of the plants as well as otherfactors that can influence the oil compositions.

Antibacterial activity (Disc diffusion test)

he in vitroantibacterial activities of the fivespecies of Ocimum essential oils and methanolextracts against the microorganism employed

and their potentials were qualitatively and quan-titatively assessed by the presence or absence ofinhibition zones and the zones diameters, MIC

values being showed in ables 3 and 4. Accord-ing to the result given in able 3, the essentialoils of O.basilicum, O. kilimandscharicum,andO. gratissimumhad a great potential of antibacte-rial activities (inhibition diameters ranged from1524 mm) against all 7 bacteria tested, whereasthose of O. canumand O. tenuiflorumhad substan-tial activities (inhibition diameters ranged from

9 mm to 22 mm) against 5 and 6 bacteria tested.On the other hand, the fractions of the methanolextracts of O. basilicum, O.kilimandscharicum ,and O. gratissimum were also found to be effectiveagainstB. subtilis, E. coli, and V. cholera out of7 bacterial species examined (inhibition diametersranged from 710 mm), respectively, probably dueto the presence of similar compounds in thesemethanol fractions, whereas those of OcimumcanumSims and Ocimum tenuiflorum L. plantsshowed no antibacterial activities (able 3). hisdisagreement can be explained by that the bet-

ter extraction of antimicrobial compounds fromvari ous medicina l plants may require differentsolvents. When compared to the methanol extracts,the essential oils exhibited a stronger and broaderactivity as compared to the methanol extract tested.Based on these results of chemical compositionof the essential oils, it is possible to concludethat the antibacterial nature of the essential oilsstudied is apparently related to their high phenoliccontents, particularly oxygenated terpenoids andphenolic terpenes, and this finding is in agreement

with previous reports (B 2004; G etal. 2009; B & J 2012). his claim is

further supported by our findings indicating highcontents of terpenoids such as citral, geraniol,eugenol, and camphor in the oils (able 2). hefindings in this study support the obser vationsof some other researchers about Ocimum speciescontaining some substances with antibacterialproperties (P et al. 1986; N et al.1999; A & O 2005; Aet al.2005; M et al.2011; V etal. 2011). However, it is difficult to compare thedata with the literature because several variablesinfluence the results, such as the environmentaland climatic conditions of the plant and the choiceof the extraction method and antimicrobial test.Moreover, standard criteria for the evaluation ofthe plant activity are missing and therefore the

results obtained by different authors are widelydifferent (R et al.1989; V B etal.1991). his is the first study to provide dataabout the extracts and essential oils of the fivespecies of Ocimumplants possessing potentialantibacterial activities as evaluated against sevenmicroorganisms. he results indicate that the es-sential oils of Ocimum species can be used as anatural source that may lead to their use as safealternatives to synthetic antimicrobial drugs. Inaddition, the data in the present study support

the use of Ocimumspecies as additives in foods,and as traditional remedies for the treatment ofinfectious diseases.

Minimum inhibitory concentration

All the essential oils tested were subjected toMIC studies against all the microorganisms. heresults in able 4 interpreted as the lowest concen-trations that inhibit the visible microbial growth.he maximal inhibition zones and MIC values for

bacterial strains, which were sensitive to the essen-tial oils of the five species of Ocimum, were in therange of 924 mm and 15.62500 g/ml (able 4).Based on these results, it is possible to concludethat the essential oils have a stronger and broaderspectrum of antimicrobial activity as comparedto the methanol extracts tested. his observationconfirmed the evidence given in a previous studyreporting that the essential oils from medicinalplants contain more antimicrobial substances thanother extracts such as water, methanol, ethanol, and

hexane exstracts (A et al.1998; E 1998).Our results also indicated in the present study that

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the O. basilicum, O. kilimandscharicum, and O. gra-tissimum essential oils were more active againstall pathogenic bacteria including Gram-negativesones than the other two essential oils, probablyowing to the high levels of phenolic compoundsin the former ones (able 2).

According to a number of studies, the Gram-positive bacteria are more sensitive to essen-tial oil than Gram-negative bacteria. A possibleexplanation may reside in the possession of anouter membrane, surrounding the cell wall ofGram-negative bacteria, thus it is logical to expectthat these bacteria wll be less susceptible to theantibacterial activity of essential oil. his outermembrane may restrict the diffusion of hydro-phobic compounds through its lipopolysaccharide

covering, presenting a barrier to the penetrationof numerous antibiotic molecule, and is alsoassociated with the enzymes in the periplasmicspace, which are capable of breaking down themolecules introduced from the outside (N1994; G et al.1999). Gram-positive bacteria donot have such an outer membrane and cell wallstructure. he antibacterial substances can easilydestroy their bacterial cell wall and cytoplasmicmembrane and cause leakage of the cytoplasmand its coagulation (K & K2003).

However, the current findings show a remarkableactivity against all gram-negative bacteria. he an-tibacterial activities of O. basilicum,O. kilimand-

scharicum, andO. gratissimum leaves extractsessential oils may be due to high contents oftannins and phenolic constituents. he mostactive constituents (essential oils) rich in phe-nolic compounds are widely reported to possesshigh levels of antimicrobial activity (P etal. 1986; N et al.1999; D &D 2000), which has been confirmed andextended in the present study, although antimi-

crobial activities of phenolic compounds mayinvolve multiple modes of action. he mode ofaction of antimicrobial agents also depends on thetype of microorganisms and is mainly related totheir cell wall structure and the outer membranearrangement. Medicinal plants contain complexphenolics and the mechanism of action of eachphenolic compound against various bacteria isalso very complicated (B 2004). herefore,it is necessary to investigate further and under-stand the relationship between the antibacterial

activity and chemical structure of each phenoliccompound in the extracts tested.

CONCLUSION

he growing tendency for replacing syntheticadditives with natural ones has brought about greatinterest in the evaluation of antimicrobial proper-ties of the plants products in both academical andindustrial fields because of their relatively safestatus, wide acceptance by consumers, and theirexploitation for potential multipurpose functionaluse. o the best of our knowledge, this is the firstreport on the in vitrocomparative evaluation ofthe antibacterial activities of the essential oils andmethanol extracts of five species of Ocimum. heessential oils of Ocimum species proved to possessinteresting properties, emerging f rom both theirchemical composition and from the evaluation of

their in vitrobiological activities. However, it isver y dif ficult to attribute the biological effect of atotal essential oil to one or a few active principles,because in addition to the major compounds,also minor compounds may make a significantcontribution to the oil activity. From the resultsgiven above, we could infer that Ocimumessentialoils, indicating strong antibacterial activities, are

very importa nt botanic al diet ar y supplementsthat can be freely used in the food industry asculinary herbs.

Acknowledgement. he authors are grateful to DS-FIS programme, Govt. of India, Department of Botany,University of Kalyani for Instrumental facilities.

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Received for publication June 11, 2012

Accepted after corrections August 22, 2012

Corresponding author

Prof. P G, Ph.D., University of Kalyani, Cytogenetics and Plant Biotechnology Research Unit,

Department of Botany, 741235, Nadia, West Bengal, India; E-mail: [email protected]

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