Escherichia coli (E. coli) is a bacterium
found in the faeces of all warm-blooded animals, including man. In
Europe and elsewhere it is used as an indicator of the sanitary
quality of bivalve shellfish.
The level of E. coli in bivalve shellfish shows how
much faecal pollution (human sewage or animal waste) they have been
exposed to in the harvesting area. This in turn determines what, if
any, treatment shellfish require before they are eaten. EU food
law stipulates monitoring, classification and resulting
There are many different methods for counting/assessing the
level of E. coli in food and environmental samples, but
not all are suitable for bivalve shellfish. Under EU Regulations a
reference method for E. coli in bivalve shellfish is
stipulated for official control testing: ISO
TS 16649-3 - Microbiology of food and animal feedings stuffs
- Horizontal method for the enumeration
Escherichia coli - Part
3: Most probable number technique
glucuronide. This reference method has been extensively
tested in bivalve shellfish and provides a reliable indicator of
the amount of faecal contamination that shellfish have been exposed
This reference method contains a specific recovery step, where
E. coli cells damaged by exposure to seawater are able to
recover. Acid production in minerals-modified glutamate broth is
used in the first stage of the method, followed by confirmation of
the presence of E. coli through β-glucoronidase production
at 44°C using a chromogenic medium. The result is expressed as a
"most probable number" (MPN) of E. coli per 100g
shellfish. The MPN technique estimates microbial population sizes
based on the pattern of positive and negative results following
incubation of replicated diluted sample, rather than counting
individual bacterial cells.
For bivalve shellfish the test is applied in a "5 by 3" format:
five replicates are tested at each of three (or more) dilutions.
This increases the method's precision, over the common "3 by 3"
For further information about sample submission, packaging
guidance, terms and conditions, and testing prices please visit
Cefas Technology Limited.
Tel: +44 (0)1305 206600
Cefas Technology Limited