Listeria mono in cold smoked salmon

[Richard Chivers]

A client who is a small producer of cold smoked Scottish salmon identified Lm in the fillets entering the factory and on a filleting knife.  No other surfaces have registered the pathogen. We have speciation but not enumeration.  These result arrived after the fish was smoked.

It has not been found on any of 3 random samples of sliced salmon (vacuum-packed and chilled at 2 centigrade).  I’m wondering about their best course of action.  On the one hand we have no evidence that there is Lm in the ready to eat product but on the other its a nightmare.  Options seem to me to:

1. Shorten the shelf life from the present 10 days to 5 from vac-packing (prior to which it is held at 1-2 centigrade for up to 5 days, but generally packed and sold within 3 days.
2. Freeze and used for an as yet unspecified cooked product in the future.
3. Destroy the batch (78 sides).

I am finding it difficult to obtain growth times at different temperatures (I have Micro-organisms in Food 5, ICMSF) in this type of substrate.  Could anyone provide data on growth at low temperatures?

With the caveat that generation time at 4C (the labelled storage temperature on release) is low, in the order of 3 days, I’m going to stick my neck out and say we can safely sell the product with a reduced shelf life of 5 days … but I stand to be corrected.  Any microbiologists have a view on this?

Kind regards

Richard