Plants have been an indispensable part of human lives either as source of food, shelter, ecological conservation and most importantly avenue for the discovery and synthesis of drugs. The use of ethno-botanical information about different plants have greatly enhanced plant research [1] and thus now provide the model for more than 50% of Western drugs [2] . Essential oils from plants have been in the forefront of tremendous breakthrough in the classification and production of products with therapeutic properties.

Struchium sparganophora is a culinary herb in most African countries. There is a severe lack of relevant scientific research carried out on this herb, despite its wide spread consumption in African countries and its ethnobotanical use. Natural products from plant origin have been a source of many novel drugs in conventional use in Health care today e.g. Artemisinin isolated from the plant Artemisia annua, sweet wormwood, a herb employed in Chinese traditional medicine and taxol from Taxus brevifola [3] . At the same time, the use of traditional medicines has increased as consumers seek complementary and or alternatives to prescribed drugs.

Plants belonging to the family Asteraceae constitute one of the largest plant families. It contains over 40 economically important species; they are used as food (lettuce and Jerusalem artichopa), oil (Sun flowers and afflower), medicine (chamomile) and many as an ornamental plant [4] .

Struchium sprganophora is a culinary herb in Nigeria. The leaves are boiled in water drained completely and added to soup or consumed as a vegetable. It is also widely used medicinally in a number of countries: decoction of the stem and root are employed in the treatment of headaches, gonorrhea [5] . The plant is an antidote for poisons [6] . In Gulf of Guinea, it is used as anti-malaria [7] while it also has anti measles activities [4] . The leaves posses nutritive, antioxidant, antimicrobial and the antimalaria activities [8] and also the anti-oxidant properties of its polar and non polar leaf extracts have been reported [9] . Phytochemical composition of the leaf and the isolation of sesquiterpine lactone, luteolin, vernodalin, 3 methyl, 2, 6 hexacosedienol from it have been reported [10] -[12] .

The objective of this study was to determine the chemical composition of the essential oils from the leaf and stem of Struchium sparganophora and their antibacterial activity.

Hydrodistillation of essential oil from leaf and stem of Struchium sparganophora gave a colourless liquid with characteristic smell of a yield of 0.15 ± 0.0% w/w and 0.08 ± 0.01% w/w respectively

The GC and GC/MS analysis of these oils resulted in the identification of 46 compounds in the leaf representing 95.3% of the oils while 55 compounds were identified in the stem representing 93.5% of the total oil as shown in table 2.

Major constituents of the essential oil from the leaf were β-caryophyllene (44.5%), humulene (5.6%), Caryophyllene oxide (4.2%), Germacrene A (3.4%) and Germacrene D (2.9%) indicating that sesquiteterpene hydrocarbon represented 61.2% of total oil.

In the stem, the major compounds were β-caryophyllene (26.1%), Caryophyllene oxide (4.9%), Humulene (4.2%), and Selinene (2.4%). This also indicated that sesquiterpene hydrocarbon accounted for 37.1% of its total oil. There was appreciable presence of methylsalicylate in both oils.

Oils from the leaf of same family Astereacea showed similarity in some type of compounds present in them but at different concentrations e.g. Vernonia scorpiodes, Vernonia migeodi and Vernonia perrotetti had β-caryophyllene and Germacrene D as part of their major constituents [18] . Comparing the oils from Struchium sparganophora with those from some members in the Asteraceae family showed they have at least two of these compounds in common. Germacrene D, β-caryophyllene and 1,8-cineole [19] -[21] .

Table 3 and Table 4 showed the result of the antibacteria assay. The essential oil from the leaf had activity against the strains as indicated by their inhibition zones. The essential oil from the stem had the highest activity

against Salmonella typhi and Peseudomonas aeruginosa but had no activity against Bacillus subtilis. The activities of both oils were higher than that of the standard Gentamycin.

Asteraceae generally have antibacterial activity [22] [23] . The activity of essential oil is related to the composition of the oil [24] , functional group and period of collection of the leaves [22] .

The antibacterial activity exhibited by the essential oil from Struchium sparganophora could be attributed to the presence of β-caryophyllene, Germacrene D, a-humulene, Caryophyllene oxide and 1,8-cineole which had been confirmed to have antibacterial activity [25] [26] .

Components are listed in order of their elution from RTX-5 column. Linear retention indices (LRI) were calculated using a homologous series C₆-C₂₈ n-alkanes. Percentage was obtained by FID peak area normalization without the use of response factor values represent the average of three measurements, n = 3. The masses (MS) were gotten by comparison of the MS with those of the computer mass libraries NIST 05 library, Wiley and Adams [13] .

We hereby acknowledge the contribution of the Staff of Department of Chemistry, Faculty of Science, University of Ibadan toward the completion of this research work.