Methods

In the UK, ISO 16649-3 ("Microbiology of the food chain - Horizontal method for the enumeration of ß-glucuronidase-positive Escherichia coli - Part 3: Detection and most probable number technique using 5-bromo-4-chloro-3-indolyl-β-D-glucuronide") is specified as the reference method for enumerating Escherichia coli (E. coli) for classifying shellfish harvesting areas and for testing products to be placed on the market (often termed end product testing). The method includes an initial resuscitation step in minerals modified glutamate broth, followed by E. coli confirmation on a chromogenic agar detecting beta-glucuronidase activity.

Alternative methods may be used if validated against the reference method using the procedures given in ISO 16140. Currently, there are two validated alternative methods for E. coli testing in live bivalve shellfish that can be used in the UK. These are the impedance and colony-count methods.

ISO 6579-1 ("Microbiology of the food chain - Horizontal method for the detection, enumeration and serotyping of Salmonella - Part 1: Detection of Salmonella spp.") is specified as the reference method for the detection of Salmonella in bivalve molluscan shellfish to be placed on the market.

NRL generic protocols for enumeration of E. coli using the MPN method, and detection of Salmonella are available to download from the information centre on this website. These protocols are compliant with the official reference methods.

Laboratories undertaking official testing of shellfish for microbiological parameters in the UK must:

  • use the reference methods or (with the agreement of the competent authority) approved alternative methods 
  • be accredited to ISO 17025 for these specific methods by an appropriate body (e.g. UKAS)
  • take part in the PHE/Cefas shellfish EQA scheme, and any relevant proficiency test distributions organised by the NRL.