Enumeration of Coliforms in Foods by the Hydrophobic Grid-Membrane Filter (HGMF) Method

HPB Method MFHPB-17
March 2001

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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.