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DOI: 10.1055/s-2007-986913
Synergistic action of extracts from carnivorous plants and synthetic peptides against plant pathogenic bacteria
Preparations from carnivorous plants e.g. Drosera spp. and Dionaea sp. (Droseraceae) were shown to possess antimicrobial properties [1]. The aim of the study was to check the bactericidal effectivity of extracts from Drosera capensis and Dionaea muscipula in combination with two synthetic peptides CAMEL (cecropin – melittin hybrid peptide) and pexiganan (magainin 2 analogue) and evaluation of a possible synergistic action. Antimicrobial activity was examined against Pectobacterium carotovorum subsp. artrosepticum (Pca), Pc subsp. carotovorum (Pcc) and Dickeya sp. (D. sp.). These are plant pathogenic bacteria responsible for significant crop losses causing e.g. soft rot and blackleg. Cultures of plants were grown on ½ MS medium (2% sucrose, pH 5.6). Quantitative and qualitative determination of naphthoquinones and flavonoids in CHCl3 and MeOH extracts was performed using NP-HPLC/UV-DAD. Plant preparations and peptides were tested for antimicrobial activity and their minimal bactericidal concentration (MBC). Values against three strains of Pca, 3 of Pcc and three strains of D. sp. were established using broth microdilution method. Extracts from both plant species with the lowest MBC values were used in combinations with peptides by a checkerboard titration method. The fractionary bactericidal concentration (FBC) index for mixtures of 2 antimicrobials was calculated according to the equation: FBC index=A/MBCA + B/MBCB, where MBCA and MBCB are the MBCs of peptide and extract separately while A and B are values for the combination of 2 compounds. The FBC indexes were interpreted as follows: <0.5, synergy; 0.5–4.0, indifferent; and >4.0, antagonism. Plant extracts tested separately were effective against all bacterial pathogens with MBC values in the range 10–50µg FW ml-1. Synergistic action of plant preparations with CAMEL was proven. The most effective combination of tested compounds was a CHCl3 extract from D. muscipula with CAMEL against Pca (FBC=0.37) and CHCl3 preparations from D. capensis with CAMEL against D.sp. (FBC=0.45).