Antibacterial and antifungal properties of neem (Azadirachta indica A. Juss)
A number of commercial neem pest control products and a laboratory prepared seed water extract were screened for antibacterial activity against bacteria with different Gram staining reactions, morphologies and pathogenicity using the agar diffusion technique. The neem component of the Trifolio-M GmbH commercial products, termed "active ingredient", and the unformulated product, MIDECOL-CF, exhibited antibacterial activity against Gram-positive and -negative bacteria including phytopathogens. The formulations of the Trifolio-M GmbH products were themselves shown to possess considerable antimicrobial activity. A Thin Layer Chromatography (TLC0 bioassay was developed using Bacillus mycoides to detect antibacterial metabolites in separated neem extracts. Three discrete zones of growth inhibition were obtained with the active ingredient indicating the presence of at least three antibacterial metabolites. TLC bioassay of laboratory prepared seed and leaf extracts resulted in considerable inhibition of B. mycoides which could not be attributed to one metabolite. No antibacterial activity was detected in pure samples of azadirachtin, nimbin or salannin. Neem callus of Ghanaian and Nigerian origin was fractionated using solid phase extraction and analysed using High Performance Liquid Chromatography (HPLC) and TLC. Both calli exhibited antibacterial activity against B. mycoides in more than one fraction although activity differed between fractions and the calli of different origins. The effect of the active ingredient on the growth of four fungal phytopathogens was investigated. Mycelial growth of Gaeumannomyces graminis var. tritic was completely inhibited in vitro although control could not be achieved in planta. Mycelial growth of Microdochium nivale was significantly reduced in vitro in the presence of the active ingredient. This extract had little effect on mycelial growth of Botrytis cinerea although MIDECOL-CF was shown to inhibit conidial germination. Activity was however lost when MIDECOL-CF was separated using TLC suggesting the presence of metabolites which act synergistically. The active ingredient inhibited conidial germination of Sphaerotheca fuliginea in vitro although no control was achieved in planta.