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#1 rosem

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Posted 20 July 2010 - 07:28 AM

Hi,

İ have a question:)

İ am working with an external laboratory. I want to believe that all results are correct so i made a sample infact very dirty sample :)

Recipe is :):):):)

Sousages, raw egg with dirty eggshell, raw fish a bit blood, mustard, unwashed vegetable & mildew chery. This delicious salad stayed 2 days in refrigaretor after stayed 1 night outside (28 degree C) .

I sent them to analyse with different name, attend to cross contamination.

And the results:

Sample 1:
1-Salmonella spp. absent within 25 g
2- Staphylococcus aureus 40 kob/g -1000 kob/g
3- Escherichia coli (kob) 60 kob/g - 10 kob/gSalmonella spp.

Sample 2:

1-Salmonella spp. absent within 25 g
2- Staphylococcus aureus 0 kob/g -1000 kob/g
3- Escherichia coli (kob) 0 kob/g -10 kob/gSalmonella spp.

Now can anyone tell me do i trust my laboratory? Change? Did i do smthng wrong?

regards...


Rose


Edited by rosem, 20 July 2010 - 01:32 PM.


#2 Gao Yu Qing

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Posted 20 July 2010 - 03:43 PM

Without knowing what bugs might have been in the mix, or if the "salad" was sufficiently mixed beforehand, I don't know if you can draw that much information from their results. Their results could be accurate or within the margin of error for the tests. Probably a better test would be to start with a sterile mix of some product, add some specific organisms you will be testing in with it and then send them in mutiple lots to be tested. You could even create a series of lots with increasing concentrations of organisms in it. That way you know beforehand what they should find, and in what ratios to eachother.
ie:
1kg of dry cereal divided into 10 identical samples.
reconstitute your test organisms in a liquid medium.
put none in your first 2 bags
1mL into your next 2
2mL into the next 2
4mL into the next 2
8mL into the next 2

Something to that effect depending on what you have on hand. that way, even if you aren't sure what total CFU's you'll get, you'll know that bags 1&2 should have close to zero or whatever your base is, 3&4 should have X, 5&6 should have 2*X, 7&8 4*X and so on. This should be a more fair way of testing the lab's accuracy.



#3 Charles.C

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Posted 20 July 2010 - 05:29 PM

Dear Rosem,

And the results:

Sample 1:
1-Salmonella spp. absent within 25 g
2- Staphylococcus aureus 40 kob/g -1000 kob/g
3- Escherichia coli (kob) 60 kob/g - 10 kob/gSalmonella spp.

Sample 2:

1-Salmonella spp. absent within 25 g
2- Staphylococcus aureus 0 kob/g -1000 kob/g
3- Escherichia coli (kob) 0 kob/g -10 kob/gSalmonella spp.



The previous post makes some valid points particularly regarding unknown homogeneity. Personally, I would have attempted, if possible, to send a sample more aligned to yr specific area of interest (?) and hopefully with a known idea of the probable (positive) level of contaminants. And preferably to 2-3 reputable laboratories, ie iso 17025 accredited, for cross-comparison. Known as a (very) small ring test.

Two samples constitutes a very small "sample" but anyway a few comments on the above data can be made. :smile:

Is this a translation from the original since some of the content seems technically rather confused.

Re No.1 - Most professional bacteriological labs IMEX do not report "absent". "Not detected" is the proper terminology assuming the result was negative.

Re No.2. Since the letters "MPN" do not appear, i presume the results are from a direct count. So what does a result like (0 - 1000)kob (col?)/g mean ?? Is this a confidence interval (very rarely reported) or what ?

Re No.3. I presume the appearance of "Salmonella" at the end is a typographical error ? The preceding data has the same criticism as No.2 above.

It would appear that the relevant lab has a number of questions to answer. :whistle:

Rgds / Charles.C

Kind Regards,

 

Charles.C


#4 Tony-C

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Posted 26 July 2010 - 04:32 AM

Hi,

İ have a question:)

İ am working with an external laboratory. I want to believe that all results are correct so i made a sample infact very dirty sample :)

Recipe is :):):):)

Sousages, raw egg with dirty eggshell, raw fish a bit blood, mustard, unwashed vegetable & mildew chery. This delicious salad stayed 2 days in refrigaretor after stayed 1 night outside (28 degree C) .

I sent them to analyse with different name, attend to cross contamination.

And the results:

Sample 1:
1-Salmonella spp. absent within 25 g
2- Staphylococcus aureus 40 kob/g -1000 kob/g
3- Escherichia coli (kob) 60 kob/g - 10 kob/gSalmonella spp.

Sample 2:

1-Salmonella spp. absent within 25 g
2- Staphylococcus aureus 0 kob/g -1000 kob/g
3- Escherichia coli (kob) 0 kob/g -10 kob/gSalmonella spp.

Now can anyone tell me do i trust my laboratory? Change? Did i do smthng wrong?

regards...


Rose


To add to the comments from Charles you may want to consider asking the Laboratory to participate in proficiency ring testing to help assess their performance.

Regards,

Tony

#5 Simon

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Posted 05 August 2010 - 07:59 AM

Should one also make sure the laboratory is competent - for example holding relevant Accredited Certification for its scope of activities?

What would that be? :dunno:


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