Antimicrobial activity of selected spices against Pectobacterium carotovorum isolated from some vegetables in Sri Lanka

Pectobacterium carotovorum is the most common causative organism of bacterial soft rot which gives rise to great economic losses. It is important to implement disease control measures and management strategies on this bacterium in order to prevent further crop loss. Among the various management strategies, using the antibacterial nature of spices offer promising solutions to pesticidal hazards and also to increasing cost of plant protection operations. Although there are many reports on the antibacterial nature of spices on various pathogens, its effect on P. carotovorum is limited. Objectives of this study were to determine the antimicrobial activity of selected spices and then to ascertain the minimum inhibitory concentration (MIC) of aqueous and ethanolic extracts of those spices against P. carotovorum. Among the nine tested spices, four were active against P. caratovorum. As depicted by agar well diffusion assay, the highest inhibitory effect on P. carotovorum was shown by the aqueous and ethanol extracts of Allium sativum while the aqueous and ethanolic extracts of Cinnamomum verum gave the smallest zones of inhibition. Garcinia cowa and Tamarindus indica displayed moderate antibacterial activity. There was no significant difference (p>0.05) in inhibition zones between aqueous and ethanol extract of a particular spice. MIC of the spices, which inhibited the growth of P. carotovorum was 0.5 g/ml within the test range. Positive extracts can be used as a cost effective and eco-friendly preventive strategy to minimize the effects of P. carotovorum. Evaluation of the antibacterial activity of these extracts under field conditions is necessary before a cost-effective formulation is developed.