Report on limits E coli O157 - not present or <10?

Hi there,

I was wondering which is more appropriate as a limit for microbes as i had an disagreement with an auditor recently.

We say our limits for E coli O157 should be <10, which in fact means due to the dilution factor = not present. The auditor was not happy with this and said it should state "not present".
I believe that this is in fact the same thing?

I would appreciate anyones opinion of this.



Thanks!

Hi There

"<10" is correct.

You have diluted a sample of a whole item. Stating "non present" is potentially ambiguous for example:

I have a cake, from which I take a 50g sample (100% cake) and dilute to 1 in 10 with a recovery diluent (10% cake).

I extract 1ml (10% cake) from the dilution and spread on my selective agar.

After incubation there are no E.coli identified.

If I then state "not present", where am I saying it is not present? within the 1ml plated?, within the dilution the 1 ml came from?, within the 50g sample?, or within the whole cake?........

The "<10" is in actuality a 'commentary' on a laboratory process and the result obtained expressed within a defined context.....

"not present" is an assumption..... maybe there were 9,8,7,6,5,4,3,2 or 1 E.coli?

Stuart

THanks Stuart!

Hi there,

I was wondering which is more appropriate as a limit for microbes as i had an disagreement with an auditor recently.

We say our limits for E coli O157 should be <10, which in fact means due to the dilution factor = not present. The auditor was not happy with this and said it should state "not present".
I believe that this is in fact the same thing?

I would appreciate anyones opinion of this.



Thanks!

Dear Tersia Claassen,

I am not surprised the auditor was unhappy.!

Perhaps you should post yr procedure since E.coli O157 is usually a "zero-tolerant" item i think.
(regardless of the statistical niceties)

Do you also state that Salmonella is < 10 (per ???)

Rgds / Charles.C

PS, a more conventional format for expressing a "negative" Salmonella sample result is something like -

"Not detected in 25g" (or 50g etc depending on the appropriate procedure)(this is normally auditorially acceptable as equatable to "absent" although some auditors will still not like it since it is statistically unrealistic as you know. Other auditors may not care since the "loose" terminology can be found in some micro. textbooks also )

But perhaps yr official procedure for O157 does not permit such a format ?.

Hi there,

I was wondering which is more appropriate as a limit for microbes as i had an disagreement with an auditor recently.

We say our limits for E coli O157 should be <10, which in fact means due to the dilution factor = not present. The auditor was not happy with this and said it should state "not present".
I believe that this is in fact the same thing?

I would appreciate anyones opinion of this.

Thanks!

Hi Tersia,

As Charles has indicated the results reported either way should be per amount in g or ml.

Assuming you can show your auditor methodology my belief is that < 10/g or ml is a more accurate report of the test result. Also maybe terminology but I see results reported as 'not detected' rather than 'not present' or 'absent' which again I think is a more accurate description.

I don't believe this should have been raised as a major issue. Was it raised in the audit report?

Kind regards,

Tony

Hi Tony,

Thanks for your imput. Yes, it was raised in the report stating: "The microbilogical specification for E coli is <10cfu/g. It is a legal requirement that E coli should be absent in ready to eat foodstuffs...."

Now firstly in South Africa, we only have GUIDELINES for microbial loads in food stuffs, so this auditor clearly has no idea....
Regards

Tersia

If you are acutally testing for the pathogen E.coli O157, then the auditor is correct.
The standard procedure for this test would be a presence/absence test and as such there would be no limit.
It is not normal to enumerate this pathogen in the lab except for research purposes. Because it has such a low infective dose, any amount of E.coli O157:H7 in a food is generally considered unacceptable.

If however, you are just trying to enumerate general E.coli levels (as an indicator of faecal contamination) than a result of <10/g or /ml is fine, depending on your dilution regime.

Note though that a result of <10 is most definitely not the same as not present. That is just an artefact of the dilutions used in testing. A sample with 9 E.coli per gram would give a result of <10, but still has the organism present.

Hi there,

I was wondering which is more appropriate as a limit for microbes as i had an disagreement with an auditor recently.

We say our limits for E coli O157 should be <10, which in fact means due to the dilution factor = not present. The auditor was not happy with this and said it should state "not present".
I believe that this is in fact the same thing?

I would appreciate anyones opinion of this.



Thanks!

OH, sorry Des, i know e coli O157 is only a confirmation, we were discussing e coli.

:)

OH, sorry Des, i know e coli O157 is only a confirmation, we were discussing e coli.

:)

Dear Tersia Claassen,

I deduce you mean that your original post contained a "typo".
(this completely changes the (legislatory) meaning of yr opening question).

As long as you appreciate that "generic" E.coli is (considerably) not the same as E.coli O157:H7.

Rgds / Charles.C

If you are acutally testing for the pathogen E.coli O157, then the auditor is correct.
The standard procedure for this test would be a presence/absence test and as such there would be no limit.

Hi Des,

I think there is a limit

Presence or Absence in an amount of product 1g or 25g, 1ml or 25ml etc.?

Because it has such a low infective dose, any amount of E.coli O157:H7 in a food is generally considered unacceptable.

How about some validation of this statement?

Regards,

Tony