9 replies to this topic

[Sharleen]

Dear all,

I'm just wondering which method you guys are applying in your companies? I am a QA analyst in a biscuit company and have been having a hard time deciding which method to use to verify the microbiological level of our finished products.

Please advise on the pros and cons on both and also have anyone actually used 1mL of inoculum on spread plate? The reason to this question is that if 0.1mL is applied on spread plate, a 10-fold dilution plate will never be obtained.

Thanks so very much everyone.

Happy 2010 in advance!

Shar

[Charles.C]

Dear Sharleen,

Biscuits not my area but personally I hv always used pour plates since all my reference procedures, BAM etc seemed to do this. However spread type may be a preferred ref. method in yr case (?). I hv attached an extract discussing pros and cons below. One option regarding yr comment about 10-fold dilution problem is mentioned though maybe impractical for routine work. (This kind of work around is also used in some official pour plate procedures, eg Staph.aureus at low levels, another variation utilises oversized petri dishes).

 pour_plate__spread_plate__pros_and_cons.xls   3.8MB   142 downloads

Best Wishes for New Year to everyone.

Rgds / Charles.C

[sudarshan]

Hi sharleen

I am using both methods .....both has advantage & disadvantage.......every microbiologist know it...in pour plate method.....needs every time prepare fresh media ....but in spread plate...prepare media once & U can use...for week...

i use 1ml for spread plate....i get proper results

Sudarshan

[poppysnoss]

Hi sharleen

I am using both methods .....both has advantage & disadvantage.......every microbiologist know it...in pour plate method.....needs every time prepare fresh media ....but in spread plate...prepare media once & U can use...for week...

i use 1ml for spread plate....i get proper results

Sudarshan

A quick query - Do you use the standard 90mm plate or the larger 140mm plate, Sudarshan? In my experience, 1ml is far too big an aliquot for a 90ml plate, as the volume of liquid to too great to properly soak into the agar and a large amount will 'go over the side'. You can't get 'even distribution.'

I use both pour plates and spread plates, obviously depending on what test is being carried out. On occassion, I will use 0.5ml for e.g. a Staphs plate, but even this is not ideal. 0.1ml is much more appropriate and is as per ISO methods.

[sudarshan]

A quick query - Do you use the standard 90mm plate or the larger 140mm plate, Sudarshan?

90MM plate.......keep plate for 5 min. approx. after inoculation....it will soak.....then invert it & keep in incubator....
i do it for meat sample for 105 dilution

Edited by sudarshan, 07 January 2010 - 12:20 PM.

[Charles.C]

Dear Sudarshan,

90MM plate.......keep plate for 5 min. approx. after inoculation....it will soak.....then invert it & keep in incubator....

I hope you hv properly validated this procedure. I can remember experimenting on something similar (not for meat) and the method gave both highly variable results and a very unappreciative lab operative .

Rgds / Charles.C

[YongYM]

Sharleen:

We use pour plate. Pipette 1ml of the first dilution (ground biscuit + diluent in 1:9) into the petri dish and pour in the melted agar. You will get the result for the first 10 fold dilution. As biscuit generally gives a very low count, so I think it is very important not to carry out too much of dilution.

Just to share with you: I try 1ml on spread plate before but it was very hard to be absorbed by the agar [I used the standard 90mm disposable plastic petri dish).


Yong

[sudarshan]

Dear Sudarshan,



I hope you hv properly validated this procedure. I can remember experimenting on something similar (not for meat) and the method gave both highly variable results and a very unappreciative lab operative .

Rgds / Charles.C

Hi Charles

I validate that procedure ......i got results proper every time ..........one day i test both way spread as well as pour for same sample & i got results for both nearly same....

[poppysnoss]

Hi Charles

I validate that procedure ......i got results proper every time ..........one day i test both way spread as well as pour for same sample & i got results for both nearly same....

Really? Well, I wouldn't allow my staff to pipette on a 90mm petri dish spread plate...and I know our accreditation bodies wouldn't allow me! Your results must have been really low counts to agree. Out of interest, which microorganism were you testing for?

[sudarshan]

Really? Well, I wouldn't allow my staff to pipette on a 90mm petri dish spread plate...and I know our accreditation bodies wouldn't allow me! Your results must have been really low counts to agree. Out of interest, which microorganism were you testing for?

Hi

I test for APC - 105 dilution,
Yeast & Mould -102,
S. Aureus - 103


Thanking you