!"#$%&" ’()* +,,-..."#$%&"/’()*(0 Full Length Research Paper Antimicrobial activity of leaves extracted samples from medicinally important Plumeria obtusa Nasir Ali 1 , Dawood Ahmad 1 , Jehan Bakht 1 *, Shahen Shah 2 , Farman Ullah 1 and Mueed-U-Rehman 3 1 Institute of Biotechnology and Genetic Engineering, Khyber Pakhtunkhwa Agricultural University, Peshawar Pakistan. 2 Department of Agronomy, Khyber Pakhtunkhwa Agricultural University, Peshawar Pakistan. 3 Department of Biotechnology, Uppsala University Sweden. Accepted 25 July, 2012 The present research work was carried out to investigate the antimicrobial (8 bacteria and 1 fungus) activities of different solvent (petroleum ether, ethyl acetate, chloroform, iso-butanol and ethanol) extracted samples from leaves of Plumeria obtusa by disc diffusion method. The data revealed that petroleum ether, iso-butanol and ethyl acetate fractions showed inhibitory activities against all the nine microbial species except Klebsiella pneumonia and Pseudomonas aeruginosa, respectively. The most susceptible gram-positive bacterium was Bacillus subtilis while the most resistant gram-positive bacterium was Staphylococcus aureus. Erwinia carotovora was the most susceptible gram-negative bacterium while P. aeruginosa was highly resistant among the gram- negative bacteria. Key words: Antimicrobial activity, solvents, fungus, disc diffusion, Plumeria obtusa. INTRODUCTION Increasing resistance of microorganisms against available antimicrobial agents is of major threat to human health and concern among scientists and clinicians world- wide. In general, it is observed that pathogenic viruses, bacteria, fungi and protozoa are becoming more difficult to treat with the available medicines (Koomen et al., 2002). To overcome the side effects of the current antimi- crobial medicines, an antimicrobial drug having a novel mode of action need to be developed (Khalafi-Nezhad et al., 2005). Medicinal plant-derived phytochemicals are large group of naturally occurring antibiotics. Recently, a considerable number of medicinal plants have been studied as potential antimicrobial agents (Harborne, 1993; Middleton and Kandaswami, 1986; Cowan, 1999; Kubmarawa et al., 2007; Bakht et al., 2011 a, b, c, d, Bakht and Shafi 2012). Presently, majority of the pharmaceutically important secondary metabolites are recovered from wild or cultivated plants as their chemical synthesis is not economically feasible (Caldentey and Inze, 2004). Major groups of antimicrobial compounds from plants include simple phenols and phenolic acids, quinones, flavones flavonoids and flavonols, tannins, coumarins, alkaloids, terpenoids and essential oils, lectins and polypeptides, and have shown in vitro activity (Cowan, 1999; Zahin et al., 2010). Therefore, such plants should be investigated for better understanding of their properties, safety and efficacy. The use of plant extracts and phytochemicals with known antimicrobial properties are very important in therapeutic treatments. In the last few years, a number of research studies have been conducted to prove such efficiency. Plumeria belongs to Apocynaceae and is a large family of about 300 genera with more than 1400 species found predominantly in tropics and sub-tropics (Dassanayake and Fosberg, 1983). Plumeria is an introduced ornamental *1(($*)#&)0 ’,+( 2%&- /$+)34+,5+"’4