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Enumeration of Coliforms in Foods and Environmental Samples Using 3m ™ Petrifilm™ High Sensitivity Coliform Count (HSCC) Plates
Laboratory Procedure MFLP-85
March 2003
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(pdf Version - 83.71 K)HEALTH PRODUCTS AND FOOD BRANCH OTTAWA
Don Warburton
Evaluation Division
Bureau of Microbial Hazards, Food Directorate
Postal Locator: 2204A1
Ottawa, ON K1A 0L2
E-mail: Don_Warburton@hc-sc.gc.ca
1. APPLICATION
This method is applicable to the enumeration of coliform bacteria in foods and environmental samples. Tolerance guidelines are specific to the product tested. This revised method replaces MFLP-85, dated October 1996.
2. PRINCIPLE
Petrifilm plates are a ready-to-use product developed by the 3M Company, St. Paul, MN 55144-1000 (USA). 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 High-Sensitivity Coliform Count (HSCC) plates. The method uses bacterial culture plates containing dry medium and a cold-water-soluble gelling agent. Undiluted or diluted samples are added directly to plates at a rate of 5.0 mL per plate. Pressure when applied to the plastic spreader placed on the overlay film, spreads the sample over a 60 cm2 growth area. The gelling agent is allowed to solidify, and the plates are incubated and then counted. Enumerated results yield a 1 coliform per gram sensitivity if a 1:5 dilution of product is made. A 2 coliform per gram sensitivity is achieved if a 1:10 dilution of product is used.
2.1 3M Microbiology is certified to ISO (International Standards Organization) 9001. Validation and collaborative studies have found the Petrifilm HSCC method to be not significantly different from the traditional methods (7.1-7.4, 7.6-7.8).
2.2 Based upon data submitted to Health Canada's Microbiological Methods Committee, the Application Section has been extended from dairy products only to include all foods and environmental samples (7.3, 7.8).
3. DEFINITION OF TERMS
3.1 See Appendix A of Volume 3.
3.2 Petrifilm HSCC plates contain Violet Red Bile (VRB) nutrients, a cold-water-soluble gelling agent, and 2, 3,5-triphenyltetrazolium chloride (TTC) indicator. The TTC indicator included in the plate is in a slow
