Quantifying of bactericide properties of medicinal plants

Extended research has been carried out to clarify the ecological role of plant secondary metabolites (SMs). Although their primary ecological function is self-defence, bioactive compounds have long been used in alternative medicine or in biological control of pests. Several members of the family Labiatae are known to have strong antimicrobial capacity. For testing and quantifying antibacterial activity, most often standard microbial protocols are used, assessing inhibitory activity on a selected strain. In this study the applicability of a microbial ecotoxtest was evaluated to quantify the aggregate bactericide capacity of Labiatae species, based on the bioluminescence inhibition of the bacterium Vibrio fischeri. Striking differences were found amongst herbs, reaching even 10-fold toxicity. Glechoma hederacea L. proved to be the most toxic, with the EC50 of 0.4073 g dried plant/l. LC50 values generated by the standard bioassay seem to be a good indicator of the bactericide property of herbs. Traditional use of the selected herbs shows a good correlation with bioactivity expressed as bioluminescence inhibition, leading to the conclusion that the Vibrio fischeri bioassay can be a good indicator of the overall antibacterial capacity of herbs, at least on a screening level.