Journal of Medicinal Plants Research Vol. 5(20), pp. 5167-5171, 30 September, 2011 Available online at http://www.academicjournals.org/JMPR ISSN 1996-0875 ©2011 Academic Journals Full Length Research Paper Antibacetial screening of leaves and stem of Carica papaya Rahman S. 1 *, Imran M. 2 , Muhammad N. 3 , Hassan N. 2 , Chisthi A. K. 1 , Khan A. F. 1 , Sadozai K. S. 1 and Khan S. M. 4 1 Department of Pharmacy, Sarhad University of Science and Information Technology, Peshawar, Pakistan. 2 School of Pharmacy, University of Lahore Islamabad-Campus. Pakistan. 3 Department of Pharmacy, University of Peshawar, Peshawar, Pakistan. 4 Riphah Institute of Pharmaceutical Sciences (RIPS), G-7/4 Islamabad, Pakistan. Accepted 12 August, 2011 The purpose of the study was to investigate antibacterial activity of ethanolic extracts of leaves and stem of Carica papaya on selected microorganisms. Various Gram negative (Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella typhi, Salmonella paratyphi A, Shigella flexenert) and Gram positive bacteria (Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Micrococcus luteus) were used for the screening of antibacterial activities of the extracts of both parts that is leaves and stem. Antibacterial activity was expressed in terms of the radius of zone of inhibition. Both parts were tested in two doses (5 and 10 mgml -1 ) it was found that the antibacterial action was dose dependent and also a significant difference was observed in bacterial sensitivity to leaves and stem extracts, however the leaves extracts were found more active than the stem. The minimum inhibitory concentration (MIC) against test microorganism was studied by turbidity method. The range of MIC observed for leaves and stem was 1250 to 5000 gml -1 and 1250 to 10,000 gml -1 respectively. C. papaya leaves and stem contains some valuable antibacterial compounds that inhibit the growth of wide variety of Gram-positive and Gram-negative organisms. Therefore the leaves and stem of C. papaya has antibacterial effects that could be useful in treating variety of bacterial infections. Key words: Carica papaya, ethanol extract, antibacterial activity, minimum inhibitory concentration. INTRODUCTION According to a research, there are 4, 22,127 plant species growing on earth; among them about 35,000 to 70,000 plants species are used as medicinal plants (Hasan et al., 2007). Out of these medicinal plants, 20,000 plants species are believed to be used medicinally in the third world (Mukherjee, 2004). Approximately 6000 species of flowering plants occur in Pakistan and 700 of them have medicinal value (Shinwari et al., 2006; Stewart, 1972). Of these species, 500 are known for their active constituents, from research conducted in Pakistan about 250 to 300 species known to have entered the herbal market of Pakistan (Williams and Ahmad, 1999). The medicinal value of plants lies in some chemical substances (plant secondary metabolites) that produce a specific biological action on the human body (Hassan et al., 2009). It is important to mention that over *Corresponding author. E-mail:shafiq_pharma01@yahoo.com. 75% of population in Pakistan is cured by using traditional medicines prescribed by more than 50,000 traditional herb practitioners (Gill, 2003) and the folk knowledge of plant curing passes down from family to family of herb practitioners and within communities (Ahmad, 2004). Carica papaya (family: Caricaceae) is a large tree-like plant with a single stem growing from 5 to 10 m (16 to 33 ft) tall with spirally arranged leaves confined to the top of the trunk. The lower trunk is conspicuously scarred where leaves and fruit were borne. The leaves are large, 50 to 70 cm diameter, deeply palmately lobed with 7 lobes. Fruits (papaya) appear on the axils of the leaves, maturing into the large 15 to 45 cm long, 10 to 30 cm in diameter fruit (Urasaki et al., 2001; Chen et al., 1987; Kim et al., 2002). Papaya fruits had extensively studied and reported for their anti fungal (Giordani et al., 2009) and antibacterial activities (Rios et al., 1988; Emeruwa, 1982). The plant is native of Tropical America and cultivated all over the tropical and subtropical countries of the world. In Pakistan it is widely