www.ijapbc.com IJAPBC – Vol. 5(3), Jul - Sep, 2016 ISSN: 2277 - 4688 303 INTERNATIONAL JOURNAL OF ADVANCES IN PHARMACY, BIOLOGY AND CHEMISTRY Research Article ABSTRACT Plants have been investigated for their antimicrobial properties and used as precursor for synthesizing medicine. Present work deals with assessing antimicrobial activity of A.cathartica against some multidrug resistant pathogenic bacteria. Different parts (leaf and flower) of A.cathartica were collected, dried and then extracted using standard methods for alkaloids, flavonoids and steroids. Extracts were then screened for antimicrobial activity using ‘Disc Diffusion Assay’. Minimum inhibitory concentration (MIC), Minimum bactericidal concentration (MBC) & Total activity were studied. Mean and Standard Deviation have also been calculated. B. subtilis found to be the most susceptible organism followed by A. tumifaciens and S. aureus. Free flavonoid extract of leaf showed the best activity against K. pneumoniae (IZ= 18mm, AI= 1±0.01, MBC= 0.156 mg/ml, MIC= 0.078 mg/ml, TA= 783.34 ml/g) followed by B. subtilis (IZ= 16mm, AI= 0.61±0.01, MBC= 0.156 mg/ml, MIC= 0.078 mg/ml, TA= 783.34 ml/g) and A. tumifaciens (IZ= 16mm, AI= 0.57±0.01, MBC= 0.156 mg/ml, MIC= 0.078 mg/ml, TA= 783.34 ml/g). Free flavonoids extract of flower also showed very good activities against A. tumifaciens (IZ= 17mm, AI= 0.71±0.01, MBC= 0.156 mg/ml, MIC= 0.078 mg/ml, TA= 399.67 ml/g) followed by B. subtilis (IZ= 16mm, AI= 0.67±0.01, MBC= 0.156 mg/ml, MIC= 0.078 mg/ml, TA= 399.67 ml/g). Bound flavonoid and alkaloid extract of leaf also showed good activities. The range of MBC and MIC was found to be 1.25-0.156mg/ml & 0.625-0.078mg/ml respectively. Results reveal that extracts of A.cathartica have good antimicrobial potential against tested microorganisms and may be exploited for future antimicrobial drugs. Keywords: Disc Diffusion Assay, MIC, MBC and Total activity. INTRODUCTION Medicinal plants are gifts of nature to cure limitless number of diseases of human beings 1 . The abundance of plants on the earth’s surface has led to an increasing interest in the investigation of different extracts obtained from traditional medicinal plants, as potential source of new antimicrobial agents 2 . Increasing failure of chemotherapeutics and antibiotic resistance exhibited by pathogenic microbial infectious agents has led to screening of several medicinal plants for their potential antimicrobial activity 3 . Hence, researchers are increasingly turning their attention to folk medicine, looking for new leads to develop better drug against microbial infections 4 . In recent years, secondary plant metabolites (phytochemicals), previously with unknown pharmacological activities, have been extensively investigated as a source of medicinal agents 5 . The natural products of higher plants may possess a new source of antimicrobial agents with possibly novel mechanisms of action 6,7 . They are effective in the treatment of infectious diseases, while simultaneously mitigating many of the side effects that are often associated with synthetic antimicrobials 8 . Therefore, it is of great interest to carry out a screening of these plants in order to validate their use in folk medicine, and to reveal the Evaluation of antimicrobial efficacy of alkaloids, flavonoids and steroids of Allamanda cathartica Linn. against some pathogenic bacteria Meenakshi Fartyal, Padma Kumar Laboratory of Plant Tissue Culture and Secondary Metabolites, Department of Botany, University of Rajasthan, Jaipur, India.