Assessment of Antibacterial Activity of Essential Oil Extracted from Leaves of Thaumatococcus danielli (Benn.) Benth. in Light of its Inhibitory Impact on Extracellular Protease of Shigella dysenteriae

Abstract

Aims: This study was carried out to assess the antimicrobial effect of the volatile oil of Thaumatococcus danielli (Benn.) Benth. leaves against selected enteric pathogens and its possible inhibition against a partially purified and characterized extracellular protease of Shigella dysenteriae. Study Design:  The volatile oil was used as antibacterial agent against eight enteric pathogens and as potential inhibitor to a partially purified extracellular protease of Shigella dysenteriae. Place and Duration of Study: Department of Biochemistry, Faculty of Science, Lagos State University, Ojo Lagos State, Nigeria; between May – September 2013. Methodology: The volatile oil was extracted by hydrodistillation. The sensitivity, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the volatile oil against the pathogens were determined by disc-diffusion and micro-dilution techniques. The extracellular protease of Shigella dysenteriae was partially purified by (NH4)2SO4 salting-out followed by gel filtration chromatography. Enzyme assay was carried out with casein (as substrate) and volatile oil (as inhibitor). Results: The average inhibition zones ranged from 16 – 30 mm. Klebsiella pneumoniae, Staphylococcus aureus and Enterococcus faecalis remained insensitive to the oil. Shigella dysenteriae and Proteus vulgaris showed highest and lowest sensitivities respectively. Highest purification fold of 2.63 with specific activity of 18.4μmol/min/mg protein were obtained after Sephadex G-75 gel filtration of the enzyme extract. The oil competitively inhibited the partially purified extracellular protease of Shigella dysenteriae with Vmax = 8.33 ∆A/min, Km = 0.85mg/ml (no inhibitor) and apparent Km´ = 1.54mg/ml (inhibitor). Optimal activities of this protease were obtained at pH 7.5 and 30ºC. Conclusion: Though, it may not be clarified whether the oil interacted with the substrate/enzyme. Nevertheless, there was an inhibition of the extracellular protease of Shigella dysenteriae by the volatile oil of Thaumatococcus danielli (Benn.) Benth. It was therefore envisaged that elaborate work on the inhibition of this type of enzyme in pathogens by essential oil would be a platform of arresting infection caused by bacteria.