MFHPB-31 Determination of Coliforms in Foods Using Violet Red Bile Agar
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FA6EB017A0C542C9B8CE3200E4136502 |
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0.03 |
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页数： |
7 |
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日期： |
2012-3-2 |
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Published on the Food Directorate’s (Health Canada's) website at http://www.hc-sc.gc.ca/food-aliment.,Government of Canada Gouvernement du Canada,HPB Method MFHPB-31,March 2001,HEALTH PRODUCTS AND FOOD BRANCH,OTTAWA,DETERMINATION OF COLIFORMS IN FOODS USING VIOLET RED BILE AGAR,Patti Wilson,Canadian Food Inspection Agency,CFIA Dartmouth Laboratory,P.O. Box 1060,Dartmouth, NS B2Y 3Z7,Wilsonpa@em.agr.ca,1. APPLICATION,This method is applicable to the enumeration of coliforms in foods and food ingredients to,determine compliance with the requirements of Sections 4 and 7 of the Food and Drugs Act.,Where an Official Method for certain products is specified, that method shall be followed. This,method is not applicable for the enumeration of coliforms in fish, fish products or other “seafood”.,This revised method replaces MFHPB-31, dated April 1997.,2. DESCRIPTION,This method has been shown to produce satisfactory results with naturally-contaminated foods,for the detection of coliforms (8.2 -8.5).,3. PRINCIPLE,The presence of coliforms in a food may indicate that it has been manufactured under unsanitary,conditions. This procedure estimates the number of viable coliforms per g or mL of product. A,portion of the product is mixed and incubated with a selective medium by the pour plate,technique. A selection of typical red-purple colonies are subjected to confirmatory tests. The,number of confirmed coliforms is calculated from the ratio of colonies confirmed to colonies,tested.,4. DEFINITION OF TERMS,See Appendix A of Volume 2.,5. COLLECTION OF SAMPLES,See Appendix B of Volume 2.,MFHPB-31,- 2 - March 2001,6. MATERIALS AND SPECIAL EQUIPMENT,The following media (1, 3 to 8) are commercially available and are to be prepared and sterilized,according to the manufacturer's instructions. See also (8.1) and Appendix G of Volume 2.,1) Peptone (0.1%) Water diluent (PW),2) 2% aqueous sodium citrate (tempered to 450C) (for cheese samples only),3) Nutrient Agar (NA),4) Tryptic Soy Agar (TSA),5) Levine's Eosin Methylene Blue (L-EMB) agar or Endo agar,6) Brilliant Green Lactose 2% Bile (BGLB) broth,7) Lauryl Sulfate Tryptose (LST) broth,8) Violet Red Bile (VRBA) Agar,9) Double Strength Violet Red Bile Agar,10) Stomacher, blender or equivalent,11) pH meter or paper capable of distinguishing to 0.3 to 0.5 pH units within a range of 5.0 to,8.0.,12) 1N HCl and 1N NaOH,13) Gram stain reagents,14) Light microscope,15) Positive and negative control cultures, ATCC or equivalent (see Table II),16) Incubator capable of maintaining 35EC,NOTE: It is the responsibility of each laboratory to ensure that the temperature of the incubators or,waterbaths are maintained at the recommended temperatures. Where 35EC is recommended in,text of the method the incubator may be 35 +/-1.0°C. Similarly, lower temperatures of 30 or 25,may be +/- 1.0EC. However, where higher temperatures are recommended, such as 43 or,45.5EC, it is imperative that the incubators or water baths be maintained within 0.5EC due to the,potential lethality of higher temperatures on the microorganism being isolated.,17) Colony counting device (optional),18) Control strains; use the suggestions listed in Table II, using ATCC or equivalent strains.,7. PROCEDURE,Each sample unit may be analyzed individually or the analytical units may be combined. Carry,out the test in accordance with the following instructions:,7.1 Handling of Samples Units,MFHPB-31,- 3 - March 2001,7.1.1 In the laboratory prior to analysis, except for shelf-stable foods, keep sample,units refrigerated (0-5oC) 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.,7.1.2 Analyze sample units as soon as possible after their receipt in the laboratory.,7.2 Preparation for Analysis,7.2.1 Have ready sterile peptone water.,7.2.2 Clean the surface of the working area with a suitable disinfectant.,7.3 Preparation of Sample,7.3.1 To ensure a truly representative analytical unit, agitate liquids or free flowing,materials until the contents are homogeneous. If the sample unit is a solid,obtain the analytical unit by taking a portion from several locations within the,sample unit. To reduce the workload, the analytical units may be combined for,analysis. It is recommended that a composite contain not more than 500 g.,7.3.2 Prepare a 1:10 dilution of the food by aseptically blending 25 g or mL (the,analytical unit) into 225 mL of the required diluent, as indicated in Table I. If a,sample size other than 25 g or mL is used, maintain the 1:10 sample to dilution,ratio, such as 11 (10) g or m……
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