Impedance method application for number detection Escherichia coli in molluscs testing by official laboratory

Abstract

Bivalve molluscan shellfish (BMS) have an important role in the transmission of some pathogens responsible for food-borne disease because they are filter-feeding animals capable of greatly concentrating certain pathogenic agents (bacteria, viruses, or parasites) present in the water column, like Escherichia coli. The reference method for E. coli testing in bivalves is the most probable number (MPN) method therefore, as this method has some disadvantages, alternative techniques of equivalent accuracy could be used without the drawbacks of the MPN method such as the direct impedance technique. This method is based on the principle that bacteria produce positively or negatively charged end products causing an impedance variation of the medium that can be used to measure their growth. The present study evaluated the efficiency of the direct impedance measuring technique through a series of laboratory tests performed on 6 kg of clams belonging to two different batches. The preliminary obtained data, compared with the MPN reference method and dd-PCR to validate the alternative method, show that the direct impedance technique has the potential to be used in place of TBX culture for confirming E. coli in MPN assays.