Correct reporting format of micro results (e.g. cfu/g or cfu/ml)

I've just been asked a very strange question with regards to how my micro results are reprted.

Our results are reported as cfu/g or cfu/ml for tests such as TVC, entros , etc

Now my lab is UKAS accredited, and i've had numerous audits from retailers, BRC etc and it's never been questioned. However i'm being audited by an european vet and one of the questions he's asked is why they report results in this way, that it should be reported as cfu/ 10g

Any suggestions?

Caz x

Hi Caz, not an easy one to answer without more insight into the vet's question, however I suspect he is working from a specific standard or microbiological criteria which states it in per 10g.

The lab on the other hand is likely making testing dilutions of the sample down to 1 ml for example and expressing the result as such. I would start with asking the vet for his/her reference. From there speak to the lab and determine the accredited method.

George

Dear Caz,

I have got accustomed to similar nuisance questions, eg whether mg/L is the same as ppm.

My immediate suspicion is that the third party is unable to mentally convert yr data into a form comparable to his specifications. Hence worried.

It may relate to a sample size of 10g if relevant to the procedure, eg absence of XYZ in.....

I agree with George's suggestions, also good chance that any available reference may not be in English or American.

Rgds / Charles

Your result depends on the amout of sample weighed and the amount of diluent used. If you weighed 10g of sample and diluted with 90ml of diluent and plated one ml then your result is cfu/g. Alternatively if you plate 1 ml directly your result will be cfu/ml. It's all down to the amount sampled and the dilution factor.
Expression of results is usually as follows. If the plate corresponding to the test sample (liquid products) or the initial suspension (other products) contains no colonies report the result as follows:

- less than 1 cfu/ml (liquid products)

- less than 1 x 10d cfu/g (other products) where d is the dilution factor of the initial suspension. If the plate contains colonies, calculate the number of microorganisms per ml or per g of product depending on the case, using the number of colonies and the appropriate dilution.

For example BS EN ISO 4833:2003 Method for the enumeration of microorganisms - Colony Count Technique @ 30°C Section 10 describes Expression of Results as do all standard methods. If you are an accredited lab I'm sure you have all the standard methods on file and these should explain the expression of results.

Hi Caz,

perhaps just a question of what should be expressed or who is expressing/expecting data?

Example: Testing chocolate for salmonella you have to take e.g. 30 times 25 g of sample (n=30). You are testing for absence i.e. 30 samples can be pooled and analysed combined. How to express the result?
absent/25 g
absent/750 g
How to include this parameter in specs ? You can use n/c/m/M or a description like above, which is common in food industry (including vets).

Rgds
moskito

Results are reported in different ways

I've just been asked a very strange question with regards to how my micro results are reprted.

Our results are reported as cfu/g or cfu/ml for tests such as TVC, entros , etc

Now my lab is UKAS accredited, and i've had numerous audits from retailers, BRC etc and it's never been questioned. However i'm being audited by an european vet and one of the questions he's asked is why they report results in this way, that it should be reported as cfu/ 10g

Any suggestions?

Caz x

Greetings All,

I can relate to the numerous interpretations a.w.a. units of measure "preferred" in reporting on analyses results. I am adamant to sustain my reporting in cfu/mL (liquid samples); cfu/g (semi-/solid product); cfu/sq.cm (hygiene efficiency checks, hand swabs and industrial effluent drain swabs).

This set the theme for my actual query: It is a Food Safety Audit-requirement to, on a pre-determined basis, compile a TREND REPORT of the numerous sets of analyses conducted.

I am NOT a statistical genius, however, have a passable understanding of the underlying principles esp. in relating the information from graphical to impact on food safety and the business.

Would a Predictive Model (Excel-based) be available for determination of (extended) shelf-life, esp. frozen Ready-to-Eat convenience meals e.g. 15 months @ minus 18 °C storage. The constraint presented is the availability of facilities and accredited analytical laboratories to assist.

Any assistance shall be highly appreciated.

Thank you,

Graham

Hi Caz,

perhaps just a question of what should be expressed or who is expressing/expecting data?

Example: Testing chocolate for salmonella you have to take e.g. 30 times 25 g of sample (n=30). You are testing for absence i.e. 30 samples can be pooled and analysed combined. How to express the result?
absent/25 g
absent/750 g
How to include this parameter in specs ? You can use n/c/m/M or a description like above, which is common in food industry (including vets).

Rgds
moskito

Results are reported in different ways

Dear moskito,

There are a lot of factors to consider if you wish to state a statistically meaningful requirement. As a result most people / specs use  “simplified” variations for which a lot  exist. And become a source of (high-powered) debate for the statistics experts .

Use of the word “absent” tends to be discouraged on statistical grounds although it is undeniably popular in the literature, together with “free of …” and “0”. which clearly sound more consumer impressive plus textually align with the zero-tolerant philosophy. FSOs and POs also occur although only rarely.

IMEX (others may disgree) the most common spec. format which I “like”  is one of three varieties –

Salmonella - Not detected in 25g (or 50g or whatever used)

Salmonella - Not detected in 25g (operational nmMc data in brackets)

Salmonella – Not detected in 25g (methodology BAM, USDA, whatever)

Use of the composite info. is possible (eg see Compendium of methods for the microbiological examination of foods, APHA, pg358-9) but IMO is more likely to confuse the routine user than enlighten.

The word “Absent” certainly appears as a substitute for “Not Detected” in many documents, books also. Preferably avoided IMO.

There is an older thread on this topic here which you may also find of interest –

http://www.ifsqn.com...000/#entry39385

Rgds / Charles.C