Chemical Composition and Biological Activities of the Essential Oil from Leaves and Flowers of Pulicaria incisa sub. candolleana (Family Asteraceae)

The composition of the essential oil isolated from leaves and flowers of Pulicaria incisa sub. candolleana E. Gamal ‐Eldin , growing in Egypt, was analysed by GC and GC‐MS. Forty‐nine and 68 compounds were identified from the oils of the leaves and flowers accounting for 86.69 and 84.29%, respectively of the total detected constituents. Both leaves and flowers oils were characterized by the high content of carvotanacetone with 66.01, 50.87 and chrysanthenone 13.26, 24.3%, respectively. The cytotoxic activity of both essential oils was evaluated against hepatocellular carcinoma cell line HEPG‐2, using MTT assay and vinblastine as a reference drug. Leaf oil showed higher activity with IC₅₀ 11.4 μg/ml compared with 37.4 μg/ml for flower oil. The antimicrobial activity of both oils was evaluated using agar well diffusion method towards two representatives for each of Gram positive and Gram negative bacteria as well as four representatives for fungi. The minimum inhibitory concentration of both essential oils against bacterial and fungal strains was obtained in the range of 0.49 – 15.63 μg/ml.     

Chemical Composition and Biological Studies of the Essential Oil from Aerial Parts of Beta vulgaris subsp. maritima (L.) Arcang. Growing in Tunisia

The chemical composition, antioxidant, cytotoxic, anticholinesterase and anti‐tyrosinase activities of the hydrodistilled essential oil of the aerial parts of Beta vulgaris subsp. maritime (L.) Arcang . from Tunisia have been evaluated. The chemical composition of the oil (yield 0.037% [w/w]), determined by GC‐FID and GC/MS is reported for the first time. Twenty five components, accounting for 98.1% of the total oil have been identified. The oil was characterized by a high proportion of oxygenated sesquiterpenes (39.2%), followed by sesquiterpene hydrocarbons (30.3%) and one apocarotenoids (26.3%). The main compounds were γ‐irone (26.3%), α‐cadinol (12.1%), T‐cadinol (10.6%), bicyclogermacrene (10.4%) and δ‐cadinene (6.0%). The isolated oil was tested for its antioxidant activity using the DPPH^·, ABTS^+·, catalase, and paraoxonase assays and also for its cytotoxic, anticholinesterase, and anti‐tyrosinase activities. The essential oil exhibited high antioxidant activity (IC₅₀ = 0.055 ± 0.006 mg/ml) and important result oncatalase (524.447 ± 2.58 Units/mg protein). Furthermore, it exerted a significant cytotoxic effect against A549 cell line, with IC₅₀ = 42.44 ± 1.40 μg/ml. The results indicate that the essential oil of B. vulgaris subsp. maritima (L.) Arcang . aerial parts may be used in future as an alternative to synthetic antioxidant agents, with potential application in the food and pharmaceutical industries.     

Secondary Metabolites,Glandular Trichomes and Biological Activity of Sideritis montana L. subsp. montana from Central Italy

Sideritis montana subsp. montana is a small annual herb occurring in countries bordering the Mediterranean and Balkan regions. The secondary metabolism of this plant has not been fully explored so far. The aim of the present study was to understand the complex mixture of secondary metabolites and the type of secretory structures. The polar constituents were isolated by column chromatography from the ethanolic extract, and their structure was elucidated by NMR and MS. The essential oil was isolated by hydrodistillation and analysed by GC/MS. The plant indumentum was studied by light and scanning electron microscopy. To complete the work, the essential oil antioxidant activity and cytotoxicity on tumor cells were evaluated by DPPH, ABTS, FRAP, and MTT methods. Four different classes of secondary metabolites were isolated, namely flavonoids, caffeoylquinic derivatives, glycosidic hydroquinones and iridoids. The essential oil was mainly characterized by sesquiterpenene hydrocarbons. Peltate and long‐capitate hairs were the main sites where terpenes and polar constituents are produced. The secondary metabolites found in S. montana subsp. montana are of chemotaxonomic interest, some of them being typical of the genus Sideritis. The trichomes types observed partially differ from those described in other members of the genus Sideritis. The essential oil showed noteworthy inhibition on tumor cells.     

Chemical Composition and Antimicrobial Activity of the Essential Oil and Methanol Extract of Hypericum aegypticum subsp. webbii (Spach) N. Robson

Hypericum aegypticum subsp. webbii is an evergreen shrub spread in Mediterranean part of central and southeastern Europe. The chemical composition and antimicrobial activity of the essential oil and MeOH extract of H. aegypticum subsp. webbii were investigated. The monoterpenes α‐pinene (63.4 – 68.5%) and β‐pinene (16.9 – 17.0%) were main compounds in the volatile oil from aerial parts. In the cluster analysis, the essential oil of H. aegypticum subsp. webbii was separated and chemically different from the oil of other subspecies of H. aegypticum as well as other Hypericum species from Greece. SIMPER analysis revealed that α‐pinene (24.79%) was the component that contributed the most to differences between all oils. Also, there was extremely high overall dissimilarity between three subspecies of H. aegypticum. MeOH extract of aerial parts of H. aegypticum subsp. webbii contained flavonoids rutin (56.4 ± 0.9 mg/g), hyperoside and quercetin, and phenolic acids chlorogenic and caffeic acid, while naphthodianthrones were not detected. The antimicrobial activity of essential oil was moderate (MIC from 100 to >200 μg/ml), while MeOH extract inhibited the growth of Gram‐positive bacteria Bacillus subtilis, Enterococcus faecalis, Staphylococcus epidermidis, and Micrococcus luteus (MIC 50 – 100 μg/ml), more pronounced than the extract of H. perforatum (MIC 200 – >200 μg/ml).     

In vitro Biological Activities of Seed Essential Oils from the Cameroonian Spices Afrostyrax lepidophyllus Mildbr. and Scorodophloeus zenkeri Harms Rich in Sulfur‐Containing Compounds

The chemical composition of the essential oils obtained from the seeds of bush onion (Afrostyrax lepidophyllus) and tropical garlic tree (Scorodophloeus zenkeri), plants used as spices in the traditional African cuisine, was determined by GC‐FID and GC/MS analyses. Moreover, in vitro biological properties of the oils, namely, the cytotoxic, antioxidant, and antimicrobial activities, were investigated by the MTT, the DPPH^. and ABTS^.+ scavenging, and the agar disc‐diffusion methods, respectively. Both oils were composed mainly by S‐containing compounds, accounting for 91.0–96.1% of the total oil compositions, which provided them the typical garlic‐ and onion‐like odors of spices. The predominant compound in both oils, 2,4,5,7‐tetrathiaoctane ( 1 ; 51.5–52.9%), was isolated by preparative TLC and structurally elucidated by ¹H‐ and ¹³C‐NMR data. The oils exhibited a strong inhibitory effect on the growth of human cancer cells, namely, T98G (human glioblastoma multiforme cell line), MDA‐MB 231 (human breast adenocarcinoma cell line), A375 (human malignant melanoma cell line), and HCT116 (human colon carcinoma cell line) cells, and a good DPPH^.‐ and ABTS^.+‐scavenging activity, while the antimicrobial effects were negligible. The volatile compositions of A. lepidophyllus and S. zenkeri oils supported their use as odorous spices. The significant inhibition activities detected make these oils worthy of further investigation as promising chemopreventive agents to be exploited in the African pharmaceutical market.     

Chemical Composition and in vitro Biological Activities of the Essential Oil of Vepris macrophylla (Baker) I.Verd. Endemic to Madagascar

Vepris macrophylla is an evergreen tree occurring in sub‐humid forest of Madagascar and traditionally used in the Island to treat several complaints as well as to prepare aromatic teas and alcoholic drinks. In the present work, the essential oil distilled from the leaves was analyzed for the first time by gas chromatography (GC‐FID) and gas chromatography/mass spectrometry (GC/MS). The major compounds were citral (56.3%), i.e., mixture of neral (23.1%) and geranial (33.2%), citronellol (14.5%), and myrcene (8.3%). The essential oil exhibited antimicrobial activity against S. aureus, P. aeruginosa, and C. albicans as determined by vapor‐diffusion assay, supporting the traditional use of the plant for preparing steam bath for the treatment of infectious diseases. The essential oil was evaluated for cytotoxic activity on human tumor cell lines by MTT (=3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl‐2H‐tetrazolium bromide) assay, showing inhibitory effects comparable to those of cisplatin, notably on MDA‐MB 231 (human breast adenocarcinoma) and HCT116 (human colon carcinoma) cell lines. Finally, the essential oil was also subjected to screening for its antioxidant activity and the free radical scavenging capacity.     

Interpopulation Variability in the Essential Oil Composition of Cistus creticus subsp. eriocephalus from Sardinia

Cistus genus is widespread in the Mediterranean regions with several species and is traditionally known as a natural remedy, but few previous phytochemical researches have been reported on Cistus species growing in Sardinia. The aim of this work was to study the interpopulation variability of the volatiles of C. creticus subsp. eriocephalus to find out the natural chemotypes of this taxon for chemotaxonomic purposes. Plant material was collected from seven wild populations in Sardinia. The oils from aerial part were obtained by hydrodistillation and analyzed by GC/MS enabling to identify 185 compounds. The seven samples showed appreciable variations in their chemical composition. MA was found almost exclusively linear hydrocarbons (85%) and MN presented fatty acids (36.97%) as major fraction. CP and MN had high quantity of non‐terpenic carbonylic compounds (63% and 69%, respectively) and in CP was found also sclareol, a well‐known antimicrobial compound. PCA analysis showed the existence of a high interpopulation variability within the essential oils of C. creticus subsp. eriocephalus growing in Sardinia. For example, MN and CP are very close to each other as CG is close to PM. BN is isolated from the others Cistus populations due to lacking essential oil. These data suggest that the basis of variation in the volatile composition of seven C. creticus subsp. eriocephalus populations depends on hybridization and that the sample without essential oil is the only one no‐hybridized.     

Essential Oil Composition of Five Thymus Species from Bulgaria

In this study, the essential oil composition of five Thymus species, belonging to Sect. Hyphodromi (A. Kerner) Halácsy – Thymus atticus Čelak., T. leucotrichus Halácsy, T. striatus Vahl, T. zygioides Griseb. and T. perinicus (Velen.) Jalas. was studied by GC/MS/FID. T. atticus, T. leucotrichus, and T. striatus were characterized by high amounts of sesquiterpenoids (57.7, 78.9 and 79.7 %, respectively) with β-caryophyllene and caryophyllene oxide as the main constituents. Aromatic compounds (61.2 %) were the most abundant group in T. zygioides essential oil, with thymol (51.2 %) as the principal component. The essential oil from the endemic species T. perinicus contained almost equal amounts of monoterpenoids (37.8 %) and aromatic compounds (36.0 %) with borneol (17.9 %) and thymol (20.9 %) as the major components. The obtained results revealed the existence of new chemotypes of T. atticus (caryophyllene oxide/β-caryophyllene), T. leucotrichus (β-caryophyllene/elemol/germacrene D) and T. striatus (β-caryophyllene/germacrene D/caryophyllene oxide). The essential oil content of endemic T. perinicus is reported for the first time. Principal component analysis (PCA) and cluster analysis (CA) were used to investigate the variations in the essential oils of different Thymus species from Sect. Hyphodromi (A. Kerner) Halácsy.     

Differential Cytotoxic Activity of Essential Oil of Lippia citriodora from Different Regions in Morocco

The aim of this work was to investigate the cytotoxic effect of the essential oil of dried leaves of Lippia citriodora (H.B. & K.) harvested in different regions of Morocco. This effect was evaluated against the P815 murine mastocytoma cell line using the MTT assay. Interestingly, this work demonstrated for the first time that these essential oils exhibited a strong cytotoxic activity against the P815 cell line, with IC₅₀ values ranging from 7.75 to 13.25 μg/ml. This cytotoxicity began early and increased in a dose‐ and time‐dependent manner. The chemical profile of these essential oils was analyzed by gas chromatography coupled to mass spectrometry. Importantly, the difference in terms of major components’ contents was not significant suggesting probably that the differential cytotoxicity between these essential oils could be attributed to the difference in the content of these essential oils in minor compounds, which could interact with each other or with the main molecules. Finally, this study demonstrated for the first time that essential oils of L. citriodora from different regions in Morocco induced apoptosis against P815 tumor cell line.     

Chemical Composition and Biological Investigations of Eryngium triquetrum Essential Oil from Algeria

The chemical composition, antibacterial and antioxidant activities of the essential oil obtained from Eryngium triquetrum from Algeria were studied. The chemical composition of sample oils from 25 locations was investigated using GC‐FID and GC/MS. Twenty‐four components representing always more than 87% were identified in essential oils from total aerial parts of plants, stems, flowers and roots. Falcarinol is highly dominant in the essential oil from the roots (95.5%). The relative abundance of falcarinol in the aerial parts correlates with the phenological stages of the plant. Aerial parts of E. triquetrum produce an essential oil dominated by falcarinol during the early flowering stage, and then there is a decrease in falcarinol and rebalancing of octanal during the flowering stage. To our knowledge, the present study is the first report of the chemical composition of E. triquetrum essential oil. Evaluation of the antibacterial activity by means of the paper disc diffusion method and minimum inhibitory concentration assays, showed a moderate efficiency of E. triquetrum essential oil. Using the DPPH method, the interesting antioxidant activity of E. triquetrum essential oil was established. These activities could be attributed to the dominance of falcarinol. The outcome of our literature search on the occurrence of falcarinol in essential oils suggests that E. triquetrum from Algeria could be considered as a possible source of natural falcarinol.     

The Chemical Diversity of Lantana camara: Analyses of Essential Oil Samples from Cuba,Nepal, and Yemen

The aerial parts of Lantana camara L. were collected from three different geographical locations: Artemisa (Cuba), Biratnagar (Nepal), and Sana'a (Yemen). The essential oils were obtained by hydrodistillation and analyzed by gas chromatography/mass spectrometry. A cluster analysis of 39 L. camara essential oil compositions revealed eight major chemotypes: β‐caryophyllene, germacrene D, ar‐curcumene/zingiberene, γ‐curcumen‐15‐al/epi‐β‐bisabolol, (E)‐nerolidol, davanone, eugenol/alloaromadendrene, and carvone. The sample from Cuba falls into the group dominated by (E)‐nerolidol, the sample from Nepal is a davanone chemotype, and the sample from Yemen belongs to the β‐caryophyllene chemotype. The chemical composition of L. camara oil plays a role in the biological activity; the β‐caryophyllene and (E)‐nerolidol chemotypes showed antimicrobial and cytotoxic activities.     

Hexane Extract of Echinops spinosissimus Turra subsp. spinosus from Tunisia: A Potential Source of Acetylated Sterols – Investigation of its Biological Activities

The hexane extract of Echinops spinosissimus Turra subsp. spinosus flower heads was analyzed for its fatty acid and sterol composition. Its physicochemical characteristics were also studied. The saponification, iodine and peroxide values were determined as 255 mg KOH/g, 42.57 g I₂/100 g and 110 m equiv. O₂/kg of oil, respectively. The oleic (C18:1; 61.14%), palmitic (C16:0; 21.36%) and linoleic (C18:2; 10.45%) acids were the dominant fatty acids. This extract was also found to contain high levels of β‐sitosterol and stigmasterol (44.97% and 34.95% of total sterols, respectively). On the other hand, the identification of terpenoid compounds was investigated by using GC/MS, which revealed fourteen major terpenoids mainly taraxasterol, lupeol, pseudotaraxasterol, lup‐22(29)‐en‐3‐yl acetate, taraxasteryl acetate, α‐amyrin, β‐amyrin, pseudotaraxasteryl acetate, hop‐20(29)‐en3‐β‐ol, α‐amirenone, along with β‐sitosterol and stigmasterol. Moreover, we have evaluated the in vitro antibacterial and antifungal activities of the unsaponifiable matter and a fraction isolated from this extract. These activities were conducted using the diffusion disc methods and broth microdilution assay. The resulted fraction from this extract showed the highest antibacterial activity with significant minimum inhibitory concentrations (MIC) values 125.0 μg/ml against Staphylococcus aureus, Micrococcus luteus and Bacillus cereus. However, it did exhibit no substantial antifungal activity.     

Composition,Antioxidant, and Cytotoxic Activities of the Essential Oils from Fresh and Air‐Dried Aerial Parts of Pallenis spinosa

This study was performed to determine the chemical composition, antioxidant and cytotoxic effects of essential oils extracted from the aerial parts of fresh (F‐PSEO) and air‐dried (D‐PSEO) Pallenis spinosa. The composition of the oils was analyzed by gas chromatography (GC) and GC/mass spectrometry, the antioxidant activity by free radical scavenging and metal chelating assays, and their cytotoxicity by a flow cytometry analysis. The primary components in both oils were sesquiterpene hydrocarbons and oxygentated sesquiterpenes. F‐PSEO contained 36 different compounds; α‐cadinol (16.48%), germacra‐1(10),5‐diene‐3,4‐diol (14.45%), γ‐cadinene (12.03%), and α‐muurolol (9.89%) were the principal components. D‐PSEO contained 53 molecules; α‐cadinol (19.26%), δ‐cadinene (13.93%), α‐muurolol (12.88%), and germacra‐1(10),5‐diene‐3,4‐diol (8.41%) constituted the highest percentages. Although both oils exhibited a weak radical scavenging and chelating activity, compared to α‐tocopherol and ascorbic acid, D‐PSEO showed a 2‐fold greater antioxidant activity than F‐PSEO. Furthermore, low doses of F‐PSEO were able to inhibit the growth of leukemic (HL‐60, K562, and Jurkat) and solid tumor cells (MCF‐7, HepG2, HT‐1080, and Caco‐2) with an IC₅₀ range of 0.25 – 0.66 μg/ml and 0.50 – 2.35 μg/ml, respectively. F‐PSEO showed a ca. 2 – 3‐fold stronger cytotoxicity against the tested cells than D‐PSEO. The potent growth inhibitory effect of the plant essential oil encourages further studies to characterize the molecular mechanisms of its cytotoxicity.     

阔叶百里香鲜、干茎叶精油成分及其抑菌效果

采用水蒸气蒸馏法和气相色谱-质谱联用技术(GC-MS)分析阔叶百里香(Thymus pulegioides)鲜、干茎叶精油含油率、化学组成及其相对含量的差异,并比较精油对链格孢(Alternaria alternata)、粉红单端孢(Trichothecium roseum)和意大利青霉(Penicillium italicum)的抑制效果。鲜、干茎叶含精油率分别为0.53%、0.37%,分别鉴定出35、40种化合物,其主要化学成分相同,均含有百里香酚(鲜样31.30%,干样26.82%)、麝香草酚甲醚、右旋龙脑和邻伞花烃等,只是相对含量略有差异;在抑菌实验中,百里香精油对链格孢菌的抑制作用最为明显,其次是意大利青霉和粉红单端孢。鲜、干阔叶百里香精油的组分较为接近,相对含量略有差异;阔叶百里香精油对3种真菌具有较好的抑制效果,且鲜样精油的抑菌效果好于干样精油。     

Chemical Variability and Biological Activities of Essential Oils of Micromeria inodora (Desf.) Benth. from Algeria

The chemical composition of the essential oils isolated from the aerial parts of Micromeria inodora (Desf .) Benth . collected in 24 Algerian localities was investigated from the first time using GC‐FID, GC/MS and ¹³C‐NMR. Altogether, 83 components which accounted for 94.7% of the total oil composition were identified. The main compounds were trans‐sesquisabinene hydrate ( 1 ; 20.9%), α‐terpinyl acetate ( 2 ; 19.8%), globulol ( 3 ; 4.9%), caryophyllene oxide ( 4 ; 4.3%), β‐bisabolol ( 5 ; 2.9%) and trans‐7‐epi‐sesquisabinene hydrate ( 6 ; 2.6%). Comparison with the literature highlighted the originality of the Algerian M. inodora oil and indicated that 1 might be used as taxonomical marker. The study of the chemical variability allowed the discrimination of two main clusters confirming that there is a relation between the essential‐oil compositions and the soil nature of the harvest locations. Biological activity of M. inodora essential oil was assessed against fourteen species of microorganisms involved in nosocomial infections using paper disc diffusion and dilution agar assays. The in vitro study demonstrated a good activity against Gram‐positive strains such as Staphylococcus aureus, Bacillus cereus, Bacillus subtilis, and Enterococcus faecalis, and moderate activity against Candida albicans. These results might be useful for the future commercial valorization of M. inodora essential oil as a promising source of natural products with potential against various nosocomial community and toxinic infections.     

Variation in Essential Oil and Bioactive Compounds of Curcuma kwangsiensis Collected from Natural Habitats

The chemical compositions of essential oils (EOs) extracted from Curcuma kwangsiensis rhizomes collected from six natural habitats in P. R. China were evaluated using gas chromatography/mass spectrometry (GC/MS). Fifty‐seven components were identified from the six EOs, and their main constituents were 8,9‐dehydro‐9‐formyl‐cycloisolongifolene (2.37 – 42.59%), germacrone (6.53 – 22.20%), and l ‐camphor (0.19 – 6.12%). The six EOs exhibited different DPPH radical‐scavenging activities (IC₅₀, 2.24 – 31.03 μg/ml), with the activity of most of EOs being much higher than that of Trolox C (IC₅₀, 10.49 μg/ml) and BHT (IC₅₀, 54.13 μg/ml). Most EOs had potent antimicrobial effects against the tested bacteria and fungus. They also exhibited cytotoxicity against B16 (IC₅₀, 4.44 – 147.4 μg/ml) and LNCaP cells (IC₅₀, 73.94 – 429.25 μg/ml). The EOs showed excellent anti‐inflammatory action by significantly downregulating expression of pro‐inflammatory cytokines, cyclooxygenase‐2, and tumor necrosis factor‐α. This study provides insight into the interrelation among growth location, phytoconstituents, and bioactivities, and the results indicate the potential of C. kwangsiensis as natural nutrients, medicines, and others additives.     

Chemical Variability,Antioxidant and Antifungal Activities of Essential Oils and Hydrosol Extract of Calendula arvensis L. from Western Algeria

The chemical composition of the essential oils and hydrosol extract from aerial parts of Calendula arvensis L. was investigated using GC‐FID and GC/MS. Intra‐species variations of the chemical compositions of essential oils from 18 Algerian sample locations were investigated using statistical analysis. Chemical analysis allowed the identification of 53 compounds amounting to 92.3 – 98.5% with yields varied of 0.09 – 0.36% and the main compounds were zingiberenol 1 (8.7 – 29.8%), eremoligenol (4.2 – 12.5%), β‐curcumene (2.1 – 12.5%), zingiberenol 2 (4.6 – 19.8%) and (E,Z)‐farnesol (3.5 – 23.4%). The study of the chemical variability of essential oils allowed the discrimination of two main clusters confirming that there is a relation between the essential oil compositions and the harvest locations. Different concentrations of essential oil and hydrosol extract were prepared and their antioxidant activity were assessed using three methods (2,2‐diphenyl‐1‐picrylhydrazyl, Ferric‐Reducing Antioxidant Power Assay and β‐carotene). The results showed that hydrosol extract presented an interesting antioxidant activity. The in vitro antifungal activity of hydrosol extract produced the best antifungal inhibition against Penicillium expansum and Aspergillus niger, while, essential oil was inhibitory at relatively higher concentrations. Results showed that the treatments of pear fruits with essential oil and hydrosol extract presented a very interesting protective activity on disease severity of pears caused by P. expansum.     

Barks Essential Oil,Secondary Metabolites and Biological Activities of Four Organs of Tunisian Calligonum azel Maire

This study is the first to investigate the chemical composition of barks essential oil (EO), secondary metabolites and biological activities of the MeOH and infusions extracts of seeds, leaves, barks and roots of Calligonum azel Maire (Polygonaceae) harvested from Tunisian desert. The gas chromatography/mass spectrometry (GC/MS) results showed the presence of fifty‐four compounds in barks EO. The major components were: viridiflorol (14.6%), α‐eudesmol (8.65%), trans‐caryophyllene (6.72%), elemol (6.63%), β‐eudesmol (6.21%). The obtained results showed that C. azel is a very rich plant in secondary metabolites. High contents in polyphenols, flavonoids and tannins were observed in both extracts of all studied organs. Significant differences were found between both extracts of the four organs. Thus, polyphenols and tannins were more abundant in leaves infusion extract, while, flavonoids showed a high level in barks extract. The antioxidant activity data demonstrated that all extracts showed strong antioxidant and radical scavenging activities. The MeOH extracts presented potential for antibacterial and antifungal activities against all tested microorganisms. The inhibition zones diameters and minimal inhibitrice concentration values were in the range of 9 – 15 mm and 2.5 – 20 μg/ml, respectively. This study demonstrated that C. azel can be regarded as an excellent plant source for natural antimicrobial agents.