Abstract: A method for determining the presence of microorganisms in a liquid sample. The liquid sample is first filtered through a filter having a pore size which is small enough to prevent passage of microorganisms through the filter but large enough to permit passage of any free reducing agents present in the sample whereby microorganisms present in the sample are retained on the filter. A chromogenic reagent having an oxidation potential such that the reagent can be reduced by microbial dehydrogenase and selected such that reduction of the chromogenic reagent yields a visibly colored product is then passed through the filter, and the filter is monitored for the formation of a visibly colored product indicative of the presence of microorganisms in the sample.

Abstract: The presence of microorganisms in a liquid sample can be determined by a method comprising the steps of (a) filtering the liquid sample through a filter having a pore size which is small enough to prevent passage of microorganisms through the filter but large enough to permit passage of any free reducing agents present in the sample whereby microorganisms present in the sample are retained on the filter; (b) passing a test solution comprising a chromogenic reagent through the filter having the retained microorganisms thereon, said chromogenic reagent having an oxidation potential such that the reagent can be reduced by microbial dehydrogenase and said chromogenic reagent being selected such that reduction of the chromogenic reagent yields a visibly colored product; and (c) monitoring the filter for the formation of a visibly colored product, wherein the formation of a visibly colored product is indicative of the presence of microorganisms in the sample.