Helpful Hints – Tips for using 3M™ Petrifilm™

Sharing ideas for testing a product can benefit everyone. That is why we have this ongoing column containing helpful tips for using 3M™ Petrifilm™ plate products.

 

Questions or useful ideas that we directly hear from you inspire many of these tips.

 

     

  • When using Petrifilm plates for environmental sampling, be sure to use thiosulfate-free letheen broth if sanitizer may be present. Letheen broth neutralizes halogen, quaternary ammonium, and acid sanitizers. Do not use diluents containing thiosulphate or sodium citrate with Petrifilm plates.

     

 

     

  • To ensure accurate results it may be necessary to adjust the pH of acidic foods before plating onto any of the Petrifilm plates for bacterial enumeration. Refer to product literature for specific instructions.

     

 

     

  • The interpretation of blue colonies without gas on Petrifilm E. coli Count plates varies by method.

     

 

AOAC Official MethodsSM (991.14 Coliform and Escherichia coli Counts in Foods – Dry Rehydratable Film Methods) state that blue colonies without gas are not counted as E. coli.

 

The AFNOR method (3M 01/04-09/92) states that blue colonies without gas maybe E. coli and should be confirmed if necessary.

 

It is important for each food processor to determine the significance of blue colonies without gas for its operation.

 

     

  • New approval: Confirmed 24-hour Eschericia coli counts in Poultry, Meat and Seafood - AOAC Official MethodsSM 998.08

     

 

     

  • Next tip - coming soon!

     

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