Enumeration Of Coliforms In Food Products And Food Ingredients Using #M^TM Petrifilm^TM Coliform Count Plates

HPB Method MFHPB-35
February 2001

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1. APPLICATION

This method is applicable for the enumeration of coliforms in food products and food ingredients.

This method may also be used for environmental sampling (see Laboratory Procedure MFLP-41A and MFLP-41B). This revised method replaces MFHPB-34, dated April 1997.

2. PRINCIPLE

Petrifilm plates are a ready-to-use product developed by the 3M Company, St. Paul, MN. Media are coated onto films, so that traditional media preparation is unnecessary, and both labour and time savings are realized. Coliforms can be enumerated on the Petrifilm Coliform Count (CC) plates. The method uses bacterial culture plates containing dry medium and a cold-water-soluble gelling agent. One mL samples are added directly to the plates. Pressure, when applied to the plastic spreader placed on the overlay film, spreads the sample over 20 cm². The gelling agent is allowed to solidify, and the plates are then incubated and counted.

Validation and collaborative studies have found the Petrifilm CC method to be not significantly different from the traditional methods (7.1 - 7.13, 7.15, 7.16).

3. DEFINITION OF TERMS

3.1 See Apendix A of Volume 2.

3.2 Petrifilm CC plates contain modified Violet Red Bile (VRB) nutrients; a cold-water-soluble gelling agent; and 2, 3, 5-triphenyl tetrazolium chloride (TTC) indicator.

3.3 Coliforms produce gas from the fermentation of lactose in the medium. The gas is trapped by the films and appears as a small bubble(s) associated with a red colony on the Petrifilm CC plate.