A newly developed assay for the quantitative determination of antimicrobial (anticyanobacterial) activity of both hydrophilic and lipophilic test compounds without any restriction

SummaryThis paper reports about a newly developed assay which enables the user to quantify and compare the antimicrobial (anticyanobacterial) activity of both hydrophilic and lipophilic test compounds without any restriction. The assay is characterised by the application of a test compound solution on a porous matrix (silica gel) in well-defined concentrations per unit area, and by the coating of this matrix by a concentrated suspension of the tested living cyanobacterium (using a spraying or a dipping technique). The organism was only applied after the complete evaporation of the solvent used for preparation of the test compound solution to avert potential influences of this solvent on micro-organisms’ viability. Toxic concentrations of a test compound caused a clearly contoured regional damage in the blue–green coloured uniform layer of the cyanobacterial test organism. The resulting regional decolourisation was readily identifiable within a species-dependant short time (e.g. for the species Arthrospira laxissima after 24 h). This newly developed assay is applied for a patent in Germany.