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Validation and comparison of methods for enumeration of faecal coliforms and Escherichia coli in bivalve molluscs

Validatie en vergelijking van methoden voor de telling van fecale bacterien van de coligroep en Escherichia coli in tweekleppige weekdieren

Synopsis

The main result of the validation study to show the equivalence of two methods for the enumeration of faecal coliforms in bivalve molluscs is that the plate count method on Mac Conkey agar was indeed found to be equivalent to the MPN method. Meaning that the Netherlands fulfilled the demands as stated in Council Directive 91/492/EC. The quality requirements of bivalve molluscs, intended for human consumption, are laid down in European legislation. One of the requirements of Council Directive 91/492/EC is that bivalve molluscs must contain less than 300 faecal coliforms or less than 230 Escherichia coli per 100 g mollusc flesh and intravalvular liquid. According to this Directive, the microbiological analyses should be performed with a Most Probable number (MPN) method, 'or any other bacteriological procedure shown to be of equivalent accuracy'. Up to 2005, the Netherlands preferred a plate count method on Mac Conkey agar. To meet the requirements it was necessary to perform a national validation study. Additional to this validation study, four procedures for the enumeration of Escherichia coli were compared. This comparison was performed as in the new European Regulation 854/2004 the quality of bivalve molluscs is only based on the number of Escherichia coli and not longer on faecal coliforms. The conclusion from this comparison study is that a plate count method can be considered as a possible alternative method for the newly prescribed MPN method for the enumeration of Escherichia coli in bivalve molluscs.
 

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