Adaptation of an [3-(4,5-dimethylthiazol-2-y1)-2,5-diphenyl tetrazolium bromide] assay to evaluate the cytotoxicity of the extracellular products of micro-organisms pathogenic to fish

Aims: Adaptation of a colorimetric assay using [3-(4,5-dimethylthiazol-2-yl )-2,5-diphenyl tetrazolium bromide] (MTT) to evaluate the cytotoxicity of t he extracellular products of microorganisms pathogenic to fish. Methods and Results: The optimal conditions for the colorimetric assay were determined and this method was compared with the trypan blue exclusion ass ay. The protein concentration of extracellular products causing the death o f 50% of the cell population (CI50) was determined. Conclusions: This assay enables quantitative and objective comparison of th e cytotoxicity of the extracellular products of micro-organisms pathogenic to fish. It was shown to be more accurate than conventional counting with t he trypan blue exclusion assay. Significance and Impact of the Study: This method may also be useful for ch aracterizing the cytotoxicity of specific components of extracellular produ cts.