Methods – Bacteriological contaminants of bivalve molluscs
EU Food Hygiene Regulations specify ISO 16649-3 ("Microbiology of 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") 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).
Alternative methods may be used if validated against the reference method using the procedures given in ISO 16140.
In the UK, use of the reference method is currently stipulated for all testing of samples taken for the classification harvesting areas. 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.
The NRL generic protocol that conforms to the requirements can be found here.
A guidance document for the use and interpretation of MPN calculators for this method can be found here.
Regulation (EC) No 2073/2005 on the microbiological criteria for foodstuffs specifies ISO 6579 as the reference method for the detection of Salmonella in bivalve molluscan shellfish to be placed on the market.
Laboratories undertaking official testing of shellfish for microbiological parameters in the UK must:
- be accredited 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.