A convenient, sensitive and rapid assay for antibacterial activity of phytoalexins

The antibacterial activity of isoflavonoid and sesquiterpenoid phytoalexins was assayed on thin layer chromatography (TLC) plates using Pseudomonas syringae pv. phaseolicola as the indicator organism in the presence of 2,3,5-triphenyl-tetrazolium chloride (TZC). Addition of glycerol to the overlay nutrient medium, as a carbon source and ultimate electron donor, facilitated the reduction of TZC to pink coloured formazans by bacterial dehydrogenases. Where bacterial growth was inhibited a colourless zone was apparent against a pink background. The test, a modified version of published protocols, gave clear, reproducible results within 24 h