Antimicrobial Potential of Callistemon lanceolatus Seed Extract and its Statistical Optimization

Plants have always been eminent source of medicinal products. Screening of the aqueous seeds extract of Callistemon lanceolatus (bottle brush) revealed its broad spectrum antimicrobial potential with an inhibition zone ranging from 13 to 28 mm against various pathogenic microorganisms. While optimizing the different parameters the antimicrobial activity was better expressed at 15 % concentration, prepared by extracting the material at 60 °C for 20 min. The extract was filtered through muslin cloth and gave best results at its natural pH. Statistical optimization by Response surface methodology enhanced the antimicrobial activity up to 1.6-fold. Minimum inhibitory concentration values of the aqueous extract of seeds of C. lanceolatus against different organisms ranged from 1-5 mg/ml. The viable cell count studies indicated a bactericidal effect against most of the pathogens. The aqueous extract was found to be relatively thermostable at 100 °C. When treated for shelf life at ambient conditions and refrigeration temperature (2-8 °C), the latter only showed a 28 % loss in antimicrobial activity. The aqueous extract was found to be biosafe when evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide reagent (MTT toxicity) assay and Ames mutagenicity assay.