In vitro evaluation of antibacterial activity of a crude aqueous extract of azadirachta indica (neem) leaves

Abstract

Neem tree is a popular medicinal plant native of India but has now spread to countries the world over including Kenya. All parts of the Neem tree, that is, the seed, leaves, hark, roots and flowers are known to exhibit antibacterial activity. Despite nemerous traditional applications in treatment of infectious diseases, there is limited laboratory data to support these therapeutic claims. Genetic and environmental variability also determine the value on Neem products thus further compounding the problem. This study was carried out to evaluate an aqueous Neem leaves extract for antibacterial activity by determining the spectrum of activity, efficacy and potency of Neem leaves from coastal Kenya. The spectrum of activity was obtained by determining the susceptibility of 24 bacterial species to the extract by disk diffusion method. The efficacy and potency of the extract were assessed by comparing the Minimum Inhibition Concentration (MIC), Minimum Bactericidal Concentration (MBC) and Time-kill values of selected bacterial species to the Neem extract with those of chlorarnpheriicol. Neems were preferred in this study as the tree is evergreen and their use would save the trees from drying unlike when roots and bark are used. Leaves would also ensure a coristartt supply of the products unlike seeds which are seasonal. Out of 107 bacterial isolates, 60.7% (110.1) were sensitive while 39.3% were resistant by disc diffusion method. Of all the gratnpositive and gram-negative isolates tested, 69,7%> (±9.3) and 56.8% (-110.3) were sensitive respectively at 5% confidence interval. The MIC and MBC for Stahh. oureus, E. coli, Sal. typhi, Ps. euroginosa and Strep. pyogenes ranged from 1._5-6.0 nrg/rid and 213 rnghzll compared to 0.0625-1.2 mg/ml and 0.106-4.8 mg/ml respectively for chloramphenicol. Univariate ANOVA on MIC and MBC indicated significant difference between the potency of chloramphenicol and Neein extract with chlorarrrplrcnicol proving to be more potent than the Neem extract against the selected organisms except Ps. aeruginosa (p==0.001-0.008). Both however showed poor bactericidal properties; they did not eliminate a population of 106 of organism on incubation for 24hrs even at concentration two times the MBC. They however, considerably suppressed growth of the organisms. The organisms that were most susceptible to the extract included; Staphylococcus aureus, Escherichia coli, Salmonella typhi and Streptocoocus pyogencs and Streptococcus faecalis. Shigella, Neisseria and Haemophilus influenza species were resistant. A methicilfn resistant strain of Staph),loccocus aureus was resistant while an hscherichia coli isolates, which had proved resistant to a battery of antibacterial agents, was s upprcssed. From the results of this study it can be i nfencd that Neem is a low potency antibacterial agent with bacteriostatic properties and a broad spectrum of activity. It exhibits antibacterial activity worthy of consideration for use in treatment of bacterial infections. The results explain its popularity in controlling bacterial infections traditionally but also indicate necessity to perform susceptibility test for all isolates as same species showed different responses with different isolates. Neem extracts would be very useful in treatment of co-infections.