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Enumeration of Total Aerobic Bacteria in Food Products and Food Ingredients Using 3MPetrifilmTM Aerobic Count Plates
4. COLLECTION OF SAMPLES
See Appendix B of Volume 2.
5. MATERIALS AND SPECIAL EQUIPMENT
1) Petrifilm Aerobic Count plates 6400/6406 (3M Canada Inc., PO Box 5757, London, ON, N6A 4T1)
A. Petrifilm AC plates. Store at or below 8 °C.
B. Plastic spreading device
C. Package insert, including instructions for use. "Interpretation Guide," available upon request.
2) Appropriate diluents: Butterfield's phosphate buffer, IDFphosphate buffer (KH2PO4 at 0.0425 g/L pH 7.2), peptone salt diluent (ISO method 6887), buffered peptone water (ISO method 6579) 0.1% peptone water, saline solution (0.85 to 0.9%), bisulfate-free letheen broth and distilled water.
Note: Do not use citrate buffer or sodium thiosulfate with the Petrifilm plate method. If citrate buffer is indicated in the standard, substitute warmed (40° - 45°C) Butterfield's phosphate buffer.
3) Stomacher, blender or equivalent.
4) Incubator capable of maintaining 32 or 35EC.
5) pH meter or paper capable of distinguishing 0.3 to 0.5 pH units within a range of 6.0 to 7.5
6) 1N NaOH
7) colony counter and/or magnified illuminator
Note: It is the responsibility of each laboratory to ensure that the temperature of the incubators or water baths are maintained at the recommended temperatures. Where 35°C is recommended in the text of the method, the incubator may be at 35 +/-1.0° C. Similarly, lower temperatures of 30 or 25°C may be +/- 1.0°C. However, where higher temperatures are recommended, such as 43 or 45.5°C, it is imperative that the incubators or water baths be maintained within 0.5EC due to potential lethality of higher temperatures on the microorganism being isolated.
6. PROCEDURE
Carry out the test in accordance with the following instructions:
6.1 Handling of Food Sample
6.1.1 Prior to analysis, except for shelf-stable foods, keep sample refrigerated (2-8 °C) or frozen, depending on the nature of the product. Thaw frozen samples in a refrigerator or under time and temperature conditions which prevent microbial growth or death.
6.1.2 Analyze samples as soon as possible after their receipt in the laboratory.
