MFLP-55 Enumeration of Faecal Coliforms in Foods by the Hydrophobic Grid-Membrane Filter (HGMF) Method
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4EF8568E78C4416EA0FFBE055E4FC534 |
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5 |
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2024-7-30 |
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Published on the Food Directorate’s (Health Canada's) website at,http://www.hc-sc.gc.ca/fn-an/res-rech/analy-meth/microbio/index_e.html,Government of Canada Gouvernement du Canada,Laboratory Procedure MFLP-55,September 1998,HEALTH PROTECTION BRANCH,OTTAWA,ENUMERATION OF FAECAL COLIFORMS IN FOODS BY THE,HYDROPHOBIC GRID-MEMBRANE FILTER (HGMF) METHOD,Microbiological Methods Committee,Microbiology Evaluation Division,Bureau of Microbial Hazards, Food Directorate,Health Products and Food Branch, Health Canada,Postal Locator: 2204A1,Ottawa, Ontario K1A 0L2,E-mail: Don_Warburton@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. The method has been shown to produce,satisfactory results with fish, ground poultry meat, black pepper, cheese and nuts (9.2). 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 faecal coliforms in other foods and food ingredients. This revised method,replaces MFLP-55, dated September 1993.,2. PRINCIPLE,The enumeration of faecal coliforms depends on formation of blue growths inside HGMF grid cells, indicative of,lactose fermentation, after incubation on m-FC agar at 44.5oC for 18-24 h. The HGMF analysis takes 24-26 hr,and yields counts that are as high, but with less random error than the tube Most Probable Number method,(8.3, 8.4). A single dilution accommodates 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 (8.3). 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 faecal coliforms that grow poorly or ferment lactose slowly in LST or,BGLB media (8.3). If necessary stressed organisms may be resuscitated for 4 hours on a non-selective,medium before being exposed to selective growth conditions.,3. DEFINITION OF TERMS,See Appendix A of Volume 3 (8.4).,4. COLLECTION OF SAMPLES,MFLP-55,September 1998,- 2 -,Published on the Food Directorate’s (Health Canada's) website at,http://www.hc-sc.gc.ca/fn-an/res-rech/analy-meth/microbio/index_e.html,See Appendix B of Volume 3 (8.4).,5. MATERIALS AND SPECIAL EQUIPMENT,1) HGMF (1600 grid-cell, 0.45 :m pore size). (Available from Gelman Sciences, Montreal, Que.).,2) Membrane filter forceps (Millipore Corp.).,3) Peptone water, 0.1% (PEP) or Peptone/Tween 80 diluent (PT).,4) Tryptic soy-magnesium sulfate agar (TSAM), if a resuscitation step is required.,5) m-FC agar plates (Commercially available; Difco Laboratories),6) Enzyme solutions (Appendix E of Volume 3; 8.4) as required for some food products.,7) Colworth Stomacher or equivalent.,8) Spreadfilter with funnel (available from Richard Brancker Research Ltd., 27 Monk St., Ottawa, Ont.),plus pipet-tip prefilters (Filtaflex Ltd., P.O. Box 1224, Almonte, Ont., or Kalyx Biosciences Inc, 20,Camelot Drive, Nepean, Ont.), or ISOGRID filtration unit (Gelman Sciences).,9) HGMF Interpreter (Model MI-200; Richard Brancker Research Ltd.) or, for manual counting,Linecounter (Gelman Sciences).,10) Water bath capable of maintaining 35-37oC.,11) Incubators capable of maintaining 25o, 35o and 44.5o±0.5oC.,6. PROCEDURE,Analyze each sample unit individually.,Carry out the test in accordance with the following instructions:,6.1 Handling of Sample Units,6.1.1 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.,6.1.2 Analyze sample units as soon as possible after their receipt in the laboratory.,6.2 Preparation for Analysis,Peptone water is adequate for many foods, but if foods contain appreciable quantities of fat (cheese,and other dairy products, ground beef, etc.) the PT diluent should be used to improve filterability.,Use PT diluent if the Spreadfilter is to be used.,6.2.1 Have ready sterile peptone water (PEP) or peptone/Tween 80 (PT) diluent, tryptic soymagnesium,sulfate agar (TSAM) plates, m-FC agar plates and enzyme solutions needed for food,product category if required (see Appendix E of Volume 3; 9.5).,6.2.2 Clean the surface of the working area with a suitable disinfectan……
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