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Culture media quality tests

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#1 Franalist

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Posted 19 March 2021 - 12:49 PM

Hello everyone, at the Lab where I work I'm in charge of making and editing official documents regarding to ISO norms. Recently, it has come to my attention that my version of this Norm states that for Dilutents such as BPW the incubation time should be 45min - 1 h at 20°C - 25°C. Is it really so? Shouldn't it have to be incubated for a longer period of time? I mean, all of the other culture media incubation times last at least 24h What we. Thank you so much for your help! 



#2 Evans X.

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Posted 19 March 2021 - 01:46 PM

Greetings Franalist,

 

It depends on the specific ISO you are using and the function you use it as. A simple example is in ISO 11133 which is the main one we use in labs and states for E. coli and BPW:

 

 

1) BPW for Escherichia coli control strains according ISO 6887 (20-25 °C / 45min -1h) for dilution (as a diluent for all enumerations of m/o for quantitive method),

2) BPW for Escherichia coli control strains according ISO 21528 (37±1 °C /18±2 h) for productivity (as pre-enrichment for Ent/ceae detection for qualitative method).

 

So it comes down to your intended result and what you try to achieve from each analysis.

 

Hope it helps!



#3 Franalist

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Posted 19 March 2021 - 02:04 PM

Thank you, 

 

I think I might have stated my question the wrong way

My greatest doubt does not involve only BPW, it is in fact more general. 

What I'm trying to find out here is how to proceed with the quality tests for productivity in Transport Media (we use PBS, Peptone water, peptone water saline...) 

Here it says (I'm reading my national version of 11133:2014, btw) that for transport media such as BPW with bromocresol the incubation time should be 45min - 1 h at 20°C - 25°C. 

We do it as follows: 

For t(0) we inoculate our agar plates right away after diluting our bacteria, then we wait for  45min - 1 h at 20°C - 25°C and inoculate another agar plate for t(1). After that we incubate both our plates plus a control plate for the exact amount of time and at the same temperature range we usually proceed with our routine analysis that involve the different kinds of transport media. 

Is this procedure wrong in any way? should we proceed differently?

 

Thank you. 


Edited by Franalist, 19 March 2021 - 02:06 PM.


#4 Evans X.

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Posted 19 March 2021 - 03:35 PM

If I understood correct now then you have a flaw there. ISO 11133 states in the section for the method of quantitive testing for transport media:

 

 

Incubate the inoculated transport medium at an appropriate temperature and time according to usage in practice or given in the specified International Standard

And the international standards it refers to are for the transportation of medical samples, so unless you have that type of samples with very specific conditions, then you have to simulate the conditions present during your transportation. IMO it states pretty clearly the incubation periods that should be used for the transport and reference medium (par. 9.3).


Edited by Evans X., 19 March 2021 - 03:36 PM.





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