Enumeration of Aeromanas Hydrophila in Prepackaged Ice and Water in Sealed Containers by the Hydrophobic Grid-Membrane Filter (HGMF) Technique

Laboratory Procedure MFLP-58B
November 1999

1. Application

This method is applicable to the enumeration of viable Aeromonas hydrophila in prepackaged ice and water in sealed containers (including mineral and spring water) to determine compliance with the requirements of Sections 4 and 7 of the Food and Drugs Act. This revised method replaces MFLP-58B, dated March 1993.

2. Principle

This hydrophobic grid-membrane filter (HGMF) method based on the method of Rippey and Cabelli (7.1) as modified by Warburton et al. (7.3). 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 (7.2). The method detects as A. hydrophila organisms which are trehalose and mannitol fermenting, oxidase positive, and hemolytic. Selective and differential agars are used to aid in isolation and identification. Further identification can be done using commercially-available identification kits and biochemical reactions.

3. Definition of Terms

See Appendix A of Volume 3.

4. Collection of Samples

4.1 See Appendix B of Volume 3.

4.2 Each sample unit shall contain at least 500 mL.

4.3 Keep the sample units refrigerated (0-4 °C) or frozen during transport, depending on the nature of the product.

5. Materials and Special Equipment

1) HGMF (1600 grid-cell, 0.45µm pore size) (ISO-GRID ^R; available from Oxoid Inc., Ottawa, ON) or equivalent.

2) Membrane filter forceps (Millipore Corp.)

3) mA-trehalose (MAT) agar