Efficacy of individual biocides and synergistic combinations

A method for quantitative estimation of the biocidal effect of compounds on microbial cells has been developed based on colony growth on solid nutrient media. The method allows for specifying a mode of action and for calculating the most effective ratio of biocides in synergistic blends. The test organism Serratia marcescens was grown in the presence of copper sulfate and kathon (2-N-octyl-4-isothiazolin-3-one) on agar medium supplemented with glucose and peptone. The approach made it possible to achieve respectively 96 and 67% decreases in effective concentrations of kathon and copper sulfate in the mixture.