8 replies to this topic

[fuse_23]

Hi,

 

I am not expert on microbiology and i want to seek help from this group.  We have this raw material that has problem in salmonella.  I have mentioned on my title with different grams tested, as we have sent our raw material to external laboratory and the results we have received from were as follows:

 

per 25g - not detected

per 125g - detected

per 250g - not detected

per 375g - not detected

 

What could be the explanation for this, hope anyone can answer.

 

Thank you in advance.  Have a nice day.

[Charles.C]

Hi,

 

I am not expert on microbiology and i want to seek help from this group.  We have this raw material that has problem in salmonella.  I have mentioned on my title with different grams tested, as we have sent our raw material to external laboratory and the results we have received from were as follows:

 

per 25g - not detected

per 125g - detected

per 250g - not detected

per 375g - not detected

 

What could be the explanation for this, hope anyone can answer.

 

Thank you in advance.  Have a nice day.

 

Hi Fuse,

 

I assume that the data reflect 4 separate determinations based on the various mentioned sample weights, each taken from the same "item".

 

Several explanations are possible but one simple one is that salmonella is not homogeneously distributed within the "item".

 

To put it another way - One sample was lucky.   (or unlucky depending on yr POV)

[SUSHIL]

What is your Raw Material.There can be lot of
Factors.
First see that if the Laboratory which has tested
the Sample, whether that laboratory has retained
that samples which are showing Salmonella
positive , and one showing salmonella Negative ,get these two samples from them then send it to
another accredited Laboratory for Salmonella
testing .
If Samples Comes out Positive or Negative then
Microbiologist of that lab can give the Possible
explaination for this problem.

Edited by SUSHIL, 19 July 2021 - 04:24 AM.

[Scampi]

Are you taking grab samples or composite samples?  

 

Ideally when dealing with a product with known issues, you are taking say, 10 grams from multiple locations within a lot, blending those together, and then taking the actual sample from that

 

Also, what method is the lab using?  Are you sure it's an accredited method?

[ebb30]

I'm a little concerned about some of the replies to this question.

 

Even if you re-test retained samples at the laboratory, there is a chance you will get negatives. As Charles C. mentioned above, it could be several factors, but the simplest one is that not only is Salmonella not evenly distributed, but it is at a very low level. You need a single viable cell for a positive test, so if there were one or two, it will not be distributed in the other samples, and it will not necessarily be in the retains either. 

 

A quick blurb about the test: generally your sample is weighed out to the desired weight of the test and then enriched with a broth. The samples are incubated overnight at ideal temperatures. So if you have a viable cell, it will be happy and reproduce. The sample will have a much greater number of bacteria the next day as a result, and will be more easily detected by laboratory methods used. It only takes a single cell. Re-testing at another laboratory and getting negative results will give you a false sense of security and you will release product that is not safe. 

[MDGMG]

1) Distribution of microbes in the product is non homogeneous, This may be the primary reason. 

2) ideal sample quantity is 25g  with Min. 5 samples from each batch. 
3) Let analysis of the same sample carried out by two microbiologist simultaneously. 
4) Check the proficiency test of the chemist.

[moskito]

I support the interpretation of non-homogeneous batch if lab failure can be excluded.

What is the raw material to be tested? 

 

We are sampling some of our raw materials with automated systems.

e.g. liquid chocolate in trucks - during loading or unloading 750 g is collected as 30x 25 g over time by automatic equipment (or 1500g as 60x 25g)

All collected samples are analysed together as one 750 g-samples in the case of salmonella because as result no growth/growth is needed, no quantification.

The result is expressed in all cases as neg in 25 g.

 

Rgds

moskito

[fuse_23]

Hi All,

 

Thank you for your inputs.  I was not able to give full details of our sample and sampling procedure.  Hope I could explain more clearer

 

We have received different batches of Shrimp powder, ranging from 500-1000kg per batch.  We will now take 300g sample x 5 cartons, then we will composite this samples and send to an accredited laboratory. We are not able to take 10ctns due to limitation in time and manpower. Does our sampling has problem too? How are we able to improve it?

 

The parameters that we ask for salmonella testing (25g, 125g, 250g, 375g), since we follow some of our customer requirements, for salmonella detetction.

[Charles.C]

Hi All,

 

Thank you for your inputs.  I was not able to give full details of our sample and sampling procedure.  Hope I could explain more clearer

 

We have received different batches of Shrimp powder, ranging from 500-1000kg per batch.  We will now take 300g sample x 5 cartons, then we will composite this samples and send to an accredited laboratory. We are not able to take 10ctns due to limitation in time and manpower. Does our sampling has problem too? How are we able to improve it?

 

The parameters that we ask for salmonella testing (25g, 125g, 250g, 375g), since we follow some of our customer requirements, for salmonella detetction.

 

Hi fuse,

 

^^^(red) the quantitative answer to yr question requires further information, eg -

 

(1) What level of confidence, Y, do you require that the level of Salmonella is less than X% ?

 

(2) What/Whose Analytical Procedure do you intend to apply to detect Salmonella ?

 

For example, here are some statistical results for (1) -

 

 Salmonella sampling.PNG   57.85KB   1 downloads

 

 Compositing of Samples for Micro testing.pdf   121.73KB   37 downloads

 

FDA's (sampling/analytical) usage of  data such as above is discussed here -

 

https://www.fda.gov/...mple-homogenate

 

https://www.fda.gov/...er-5-salmonella