THE ANTIBACTERIAL ACTIVITY OF AZADARICHTA INDICA (NEEM PLANT)
Screening of medicinal plants for bioactive compounds leads to development of less expensive new antimicrobial
agents with improved safety and efficacy. Azadirachta Indica (neem) is a multipurpose tree with multiple health
benefits. Different parts of the plant are shown to exhibit antimicrobial effects against a wide variety of microor-
ganisms. In the present study we compared the antimicrobial efficacy of aqueous extracts of leaf, bark and seeds
of A. Indica against human pathogenic bacteria (Staphylococcus aureus, Enterococcus feacalis, Proteus mirabilis
and Pseudomonas aeuroginosa) and fungi (Aspergillus fumigatus and Candida albicans). Agar well diffusion me-
thod and micro-broth dilution methods were used to determine the minimum inhibitory concentration (MIC). Re-
sults showed that leaf extract exhibited strong antimicrobial activity against bacteria and fungi at all the concen-
trations tested (500, 1000 and 2000µg/ml). Antimicrobial activity of bark extract was found to be moderate on
bacteria and fungi (effective at 1000 and 2000µg/ml), whereas seed extract exhibited least antimicrobial activity.
Minimum inhibitory concentration (MIC) of leaf and bark extract was found to be in the range of 500 to
2000µg/ml for all the tested microorganisms, where as the seed extract did not inhibit the microorganisms at all
the concentrations tested except Candida albicans (1000µg /ml). Our results suggest that aqueous extracts of
Azadirachta Indica leaf and bark exhibit high antimicrobial activity.
Keywords: Azadirachta Indica; agar well diffusion method; antimicrobial; MIC; pathogenic microorganisms
Drug resistance is a serious global problem, and spread of resistance poses additional challenges for clinicians
and the pharmaceutical industry. Use of herbal medicines in the developed world continue to rise because
they are rich source of novel drugs and their bioactive principles form the basis in medicine, nutraceuticals, pharmaceutical intermediates and lead compounds in synthetic drugs (De N et al 2002 and Ncube N S et al 2008). Screening medicinal plants for biologically active compounds offers clues to develop newer antimicrobial agents. These compounds after possible chemical manipulation provide new and improved drugs to treat the infectious diseases (Natarajan et al 2003, Shah et al 2006). Plant based products/ extracts are cheaper alternatives to the development of synthetic drugs. Azadirachta Indica (A. Indica) belongs to the family Meliaceae, commonly known as neem. It is used in traditional medicine as a source of many therapeutic agents. A. indica (leaf, bark and seed) are known to contain antibacterial, antifungal activities against different pathogenic microorganisms and antiviral activity against vaccinia, chikungunya, measles and coxsackie B viruses (Biswas K et al 2002). Different parts of neem (leaf, bark and seed oil) have been shown to exhibit wide pharmacological activities including; antioxidant, antimalarial, antimutagenic, anticarcinogenic, anti-inflammatory, antihyperglycaemic, antiulcer and anti-
diabetic properties (Talwar et al 1997). The biological activities are attributed to the presence of many bioac-
tive compounds in different parts. Antimicrobial activity has been investigated for neem leaves, bark and seed, but there are no studies on the comparative evaluation of aqueous extract of leaves, bark and seed. Hence, the current study was designed to investigate the comparative antimicrobial activity of neem leaves, bark and seed aqueous extract against human pathogenic bacteria and fungi. A number of factors such as, thickness and uniformity of the gel, size of the inoculum, temperature and pH that affect the accuracy and reproducibility of the agar diffusion method were also taken into consideration to obtain reliable results.
MATERIALS AND METHODS
Collection of raw materials and preparation of ex-tracts The leaves, bark and fruits of Azadirachta Indica were collected locally and authenticated by a botanist, Ayur-
veda pharmacy, Tirupati, Andhra Pradesh. Fruits were manually separated into their seeds and seed hulls
(kernels) were milled prior to extraction. Raw materials (leaves, bark and seed) were cleaned, shade dried for
one week and pulverized to coarse powder. Approx
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