Amperometric determination of viable cell numbers based on sensing microbial respiration

Viable cell numbers were determined with an electrode system composed of a membrane filter for retaining microorganisms and an oxygen electrode. The principle of the cell number determination is based on sensing microbial respiration. The response time of the system was 10 min. A linear relationship was obtained between the current and the cell numbers of Escherichia coli, Bacillus subtilis, Flavobacterium arabrescence, Saccharomyces cerevisiae, and Trichosporon cutaneum on the membrane filter. The current was reproducible, with an average relative error of 5% when the electrode contained 2×10⁸Escherichia coli. A good agreement (a correlation coefficient; 0.98 in 10 experiments) was obtained, when the cell populations of E. coli were determined by the proposed method and colony counts. The minimum measurable cell populations were 10⁶ cells per ml with the bacteria and 10⁵ cells per ml with the yeasts.