Development of an electrochemical method for the rapid determination of microbial concentration and evidence for the reaction mechanism

Abstract A rapid amperometric method for the determination of microbial concentration is described. The micro-organisms reduce the redox mediator, potassium hexacyanoferrate(III), which is reoxidized to yield a current proportional to the microbial concentration. Escherichia coli gave a linear response (standard error ( S YX )=0.17, r =0.9999, n =5, P >99.9%) over the concentration range 10 6 –10 8 cells ml −1 with a response time of less than 1 min. The effect of varying temperature showed that the electrochemical response of the bacteria was linked to respiration rate. Studies with respiratory inhibitors suggested that hexacyanoferrate (III) is reduced by the segment of the respiratory chain between nicotinamide adenine dinucleotide (NADH) dehydrogenase and the terminal oxidases.