MFHPB-17 Enumeration of Coliforms in Foods by the Hydrophobic Grid-Membrane Filter (HGMF) Method
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8F745E20EC094FFB92E2A5BBDAB42131 |
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0.03 |
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页数： |
6 |
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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-17,March 2001,HEALTH PRODUCTS AND FOOD BRANCH,OTTAWA,ENUMERATION OF COLIFORMS IN FOODS BY THE,HYDROPHOBIC GRID-MEMBRANE FILTER (HGMF) METHOD,P.I. Peterkin, A.N. Sharpe, and H. Wang,Microbial Research Division,Bureau of Microbial Hazards,Health Products and Food Branch,Postal Locator: 2204A2,Ottawa, Ontario, K1A 0L2,E-mail: Haiyan_Wang@hc-sc.gc.ca,1. APPLICATION,The method may be used for enumeration of faecal coliform organisms in foods to determine compliance,with the requirements of Sections 4 and 7 of the Food and Drugs Act. This revised method replaces,MFHPB-17, dated April 1997.,2. DESCRIPTION,The method has been shown to produce satisfactory results with ground meat, luncheon meat, dried foods,cheese, frozen foods (9. 3) and with non-fat dry milk, canned vanilla custard, fish, poultry, nuts and pepper,(9.4). On the basis of data obtained with the latter products, the HGMF method was granted Official Final,Action status by the Association of Official Analytical Chemists (9.1). There is no reason to believe that the,method cannot be used successfully for the enumeration of coliforms in other foods and food ingredients.,3. PRINCIPLE,The HGMF analysis takes 24-26 h and yields counts that are as high as, and more precise than, the Most,Probable Number method (9.4). A single dilution gives an accurate count over a wide range of,contamination levels. Counting precision may be better than on conventional plates or membrane filters,because the HGMF reduces the effect of individual visual acuity on the count (9.5). If a low count is,expected, the detection limit can be lowered by filtering more of the suspension.,The HGMF method is capable of detecting coliforms that grow poorly or ferment lactose slowly in LST or,BGLB media (9.4). If necessary, stressed organisms should be resuscitated for 4 h on a non-selective,medium before being exposed to selective growth conditions.,4. DEFINITION OF TERMS,See Appendix A of Volume 2.,MFHPB-17,March 2001,-2-,5. COLLECTION OF SAMPLES,See Appendix B of Volume 2.,6. MATERIALS AND SPECIAL EQUIPMENT,The media listed below (items 3-5) are commercially available and are to be prepared and sterilized,according to the manufacture's instructions.,1) HGMF (1600 grid-cell, 0.45 μm pore size; available as ISO-GRID Membrane Filters from Oxoid Ltd.,Nepean, Ont.) or equivalent,2) Membrane filter forceps,3) Peptone water, 0.1% (PW) or Peptone/Tween 80 diluent (PT) (if spreadfilter is to be used),4) Nutrient agar (NA) plates, if a resuscitation step is required,5) m-FC agar plates (without rosolic acid),6) Enzyme solutions (Appendix E of Volume 2; 9. 6) as required for some food products,7) Stomacher or equivalent,8) Stomacher bags (commercially available) with interior filter or pipet-tip prefilters (Filtaflex Ltd.,Almonte, Ont.),8) Spreadfilter with funnel (Filtaflex) or ISO-GRID filtration unit (Oxoid) or equivalent,9) Incubators capable of maintaining 35 oC,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 35EC is recommended in the text,of the method, the incubator may be at 35 +/-1.0E 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 potential lethality,of higher temperatures on the microorganism being isolated.,Optional,11) Manual or automated colony counting devices,7. PROCEDURE,Analyze each sample unit individually.,Carry out the test in accordance with the following instructions:,7.1 Handling of Sample Units,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.,MFHPB-17,March 2001,-3-,7.2 Preparation for Analysis,7.2.1 Have ready sterile peptone water ( PW) or peptone/tween 80 (PT) diluent, nutrient agar,(NA) plates (if necessary), m-FC agar plates and enzyme solutions needed for food product,category if required (see Appendix E of Volume 2). Use PT diluent if the Spreadfilter is to,be used.,7.2.2 Clean the surface of the working area with a suitable disinfectant.,7.2.3 Mark clearly the dupli……
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