Adaptation of an [3‐(4,5‐dimethylthiazol‐2‐yl)‐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 the extracellular products of micro-organisms 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 assay. The protein concentration of extracellular products causing the death of 50% of the cell population (CI50) was determined. Conclusions: This assay enables quantitative and objective comparison of the cytotoxicity of the extracellular products of micro-organisms pathogenic to fish. It was shown to be more accurate than conventional counting with the trypan blue exclusion assay. Significance and Impact of the Study: This method may also be useful for characterizing the cytotoxicity of specific components of extracellular products.